Problem solving tutor Next This presentation is designed to develop your problem solving skills in quantitative chemistry. Working through the whole tutor program you will develop and use three techniques for problem solving. These have been called: 1. Knowing what you know (do this one first) 2. Tabulating the information (do this one second) 3. Storyboarding (do this one last) You are about to start: Knowing what you know

Some important points: You will need to use a calculator (or the calculator function on your computer/device). Do not use the keyboard to advance or go back through slides. Use the mouse/screen tap and the icons: Next Back Next

Problem solving tutor: Knowing what you know and don’t know Next

Knowing what you know and don’t know Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Next In the next slide you will be given a typical quantitative chemistry problem to solve. A very powerful technique is to sort the information into “what I know now”, “what I can immediately work out” and “what I have been asked for” – this will point the way through the calculation. You will do this sorting on screen here, but should do it in your head or on paper when you use this skill afterwards.

Knowing what you know and don’t know Question cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3. Next

Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. concentration of NaOH = mol dm -3 volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of H 2 SO 4 (mol) moles of NaOH (mol) What I know now (specific to this question) volume of NaOH = dm 3 What I have been asked for What I can immediately work out Info Click on the correct group of items of info to move them to the “What I know now” box, then click Next.

What I know now feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) The question tells you the volume and concentration of NaOH as well as the volume of H 2 SO 4. Keeping a clear record of what you know from a question is a key part of the skill we are learning here. Back

Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm concentration of H 2 SO 4 (mol dm -3 ) moles of H 2 SO 4 (mol) moles of NaOH (mol) What I know now (specific to this question) What I have been asked for What I can immediately work out Info Click on the correct group of items of info to move them to the “What I know now” box, then click Next. Next volume of NaOH = dm 3 concentration of NaOH = mol dm -3 volume of H 2 SO 4 = dm 3 mole ratio of NaOH : H 2 SO 4

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. concentration of H 2 SO 4 (mol dm -3 ) moles of H 2 SO 4 (mol) moles of NaOH (mol) What I have been asked for What I can immediately work out Info Click on the correct item of info to move it to the “What I have been asked for” box, then click Next. Next volume of NaOH = dm 3 concentration of NaOH = mol dm -3 volume of H 2 SO 4 = dm 3 mole ratio of NaOH : H 2 SO 4

What I have been asked for feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back The question asks you to calculate the concentration of H 2 SO 4. It is important to remember what you have been asked for as this will determine what you work out as the steps towards this.

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. moles of H 2 SO 4 (mol) moles of NaOH (mol) What I have been asked for What I can immediately work out Info Click on the correct item of info to move it to the “What I have been asked for” box, then click Next. Next volume of NaOH = dm 3 concentration of NaOH = mol dm -3 volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) mole ratio of NaOH : H 2 SO 4

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. moles of H 2 SO 4 (mol) moles of NaOH (mol) What I have been asked for What I can immediately work out Info Click on the correct item of info to move it to the “What I can immediately work out” box, then click Next. Next volume of NaOH = dm 3 concentration of NaOH = mol dm -3 volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) mole ratio of NaOH : H 2 SO 4

What I can immediately work out feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back The question has given you enough information to calculate the number of moles of NaOH but you do not yet have enough information to calculate anything more about the H 2 SO 4.

What I can immediately work out feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back We will calculate the mole ratio once we have the number of moles of NaOH.

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. moles of H 2 SO 4 (mol) What I have been asked for What I can immediately work out Info Click on the correct item of info to move it to the “What I can immediately work out” box, then click Next. Next volume of NaOH = dm 3 concentration of NaOH = mol dm -3 volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH (mol) mole ratio of NaOH : H 2 SO 4

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3. moles of H 2 SO 4 (mol) What I have been asked for What I can immediately work out Info Well done. Now select the correct calculation to calculate the number of moles of NaOH, then click Next. Next volume of NaOH = dm 3 concentration of NaOH = mol dm -3 volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH (mol) Calculation / x x mole ratio of NaOH : H 2 SO 4

Moles of NaOH feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back To calculate the number of moles of NaOH use moles = concentration x volume.

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. moles of H 2 SO 4 (mol) What I have been asked for What I can immediately work out Info Well done. Now select the correct calculation to calculate the number of moles of NaOH, then click Next. Next volume of NaOH = dm 3 concentration of NaOH = mol dm -3 volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH (mol) Calculation / x x mole ratio of NaOH : H 2 SO 4

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. moles of H 2 SO 4 (mol) What I have been asked for What I can immediately work out Info Well done. Now select the group items of information that you have used, to be moved to the bin to make room for the latest information, then select what to immediately work out. Next volume of NaOH = dm 3 concentration of NaOH = mol dm -3 volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH (mol) x moles of NaOH = mol mole ratio of NaOH : H 2 SO 4

Used item feedback Back You used the equation: moles = concentration x volume (dm 3 ) So the items you used were the concentration and volume of NaOH.

volume of NaOH = dm 3 concentration of NaOH = mol dm -3 What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. moles of H 2 SO 4 (mol) What I have been asked for What I can immediately work out Info Next volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH = mol mole ratio of NaOH : H 2 SO 4 Well done. Now select the group items of information that you have used, to be moved to the bin to make room for the latest information then select what to immediately work out.

What I can immediately work out feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back In order to calculate the number of moles of H 2 SO 4 you need to work out the mole ratio.

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. moles of H 2 SO 4 (mol) What I have been asked for What I can immediately work out Info Well done. Now select the correct mole ratio of NaOH : H 2 SO 4 then click Next. Next volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) mole ratio of NaOH : H 2 SO 4 moles of NaOH = mol Mole ratio from the balanced equation 2NaOH + H 2 SO 4  Na 2 SO 4 + 2H 2 O 1 : 2 2 : 1 1 : 1

Mole ratio feedback Back The equation is: 2NaOH + H 2 SO 4  Na 2 SO 4 + 2H 2 O The mole ratio comes from the balancing numbers – so the ratio NaOH : H 2 SO 4 : Na 2 SO 4 : H 2 O = 2 : 1 : 1 : 2 From this you can get the NaOH : H 2 SO 4 mole ratio.

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. moles of H 2 SO 4 (mol) What I have been asked for What I can immediately work out Info Well done. Now select the correct mole ratio of NaOH : H 2 SO 4 then click Next. Next volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH = mol Mole ratio from the balanced equation 2NaOH + H 2 SO 4  Na 2 SO 4 + 2H 2 O 1 : 2 2 : 1 1 : 1 mole ratio of NaOH : H 2 SO 4

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. moles of H 2 SO 4 (mol) What I have been asked for What I can immediately work out Info Well done. Now select the next item to work out, then click Next. Next volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH = mol mole ratio of NaOH : H 2 SO 4 2 : 1

What I can immediately work out feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back In order to calculate the concentration of H 2 SO 4 you need to work out the number of moles of H 2 SO 4.

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. What I have been asked for What I can immediately work out Info Well done. Now select the next item to work out, then click Next. Next volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH = mol mole ratio of NaOH : H 2 SO 4 2 : 1 moles of H 2 SO 4 (mol)

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. What I have been asked for What I can immediately work out Info Well done. Now select the correct calculation to work out the number of moles of H 2 SO 4, then click Next. Next volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH = mol mole ratio of NaOH : H 2 SO 4 2 : 1 moles of H 2 SO 4 (mol) Calculation / x x

Moles of H 2 SO 4 calculation Back Since the mole ratio is NaOH : H 2 SO 4 2 : 1 you need to divide the number of moles of NaOH by 2.

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. What I have been asked for What I can immediately work out Info Well done. Now select the correct calculation to work out the number of moles of H 2 SO 4, then click Next. Next volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH = mol mole ratio of NaOH : H 2 SO 4 2 : 1 moles of H 2 SO 4 (mol) Calculation / x x moles of H 2 SO 4 = mol

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. What I have been asked for What I can immediately work out Info Well done. Now select the item of information that you have not used, in “What I know now”, to keep – the rest will be moved to the bin to make room for the latest information – then click Next. Next volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH = mol mole ratio of NaOH : H 2 SO 4 2 : 1 moles of H 2 SO 4 = mol

Used item feedback Back You have not used the volume of H 2 SO 4 (aq).

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. What I have been asked for What I can immediately work out Info Well done. Now select the item of information that you have not used, in “What I know now” to keep – the rest will be moved to the bin to make room for the latest information – then click Next. Next volume of H 2 SO 4 = dm 3 concentration of H 2 SO 4 (mol dm -3 ) moles of NaOH = mol mole ratio of NaOH : H 2 SO 4 2 : 1 moles of H 2 SO 4 = mol

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. What I can immediately work out = Info Well done. Now select the correct calculation to work out the concentration of H 2 SO 4, then click Next. Next volume of H 2 SO 4 = dm 3 What I have been asked for concentration of H 2 SO 4 (mol dm -3 ) moles of H 2 SO 4 = mol Calculation / / x / What I have been asked for concentration of H 2 SO 4 (mol dm -3 )

Concentration feedback Back You can calculate the concentration by using moles / volume (dm 3 ).

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. What I can immediately work out = Info Well done. Now select the correct calculation to work out the concentration of H 2 SO 4, then click Next. Next volume of H 2 SO 4 = dm 3 moles of H 2 SO 4 = mol Calculation / / x / What I have been asked for concentration of H 2 SO 4 (mol dm -3 )

What I know now (specific to this question) Q cm 3 of mol dm -3 sodium hydroxide solution required 31.0 cm 3 of sulfuric acid to change the colour of the methyl orange indicator from yellow to red. Calculate the concentration of sulfuric acid in mol dm -3.. Info Well done. You now know what you were asked for: the concentration of H 2 SO 4. To move on, click Next. Next volume of H 2 SO 4 = dm 3 moles of H 2 SO 4 = mol What I can immediately work out = What I have been asked for concentration of H 2 SO 4 (mol dm -3 ) / concentration of H 2 SO 4 = mol dm -3

Well Done! You have completed the question. Keeping track of what you know and therefore what you can immediately work out is an important skill in problem solving. You should develop your skills to the point where you are doing this automatically in your head. Next question

Knowing what you know and don’t know Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Next Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction).)

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) moles of Zn (mol) What I know now What I have been asked for What I can immediately work out Info moles of H 2 (mol) mole ratio of Zn : H 2 A r of Zn = 65.4 Click on the correct group of items of info to move them to the “What I know now” box. Volume of H 2 = 1.53 dm 3 Mass of impure zinc = 5.84 g Percentage purity

What I know now feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back The question tells you the volume of hydrogen produced and the mass of impure zinc. You also know the relative atomic mass of zinc. Keeping a clear record of what you know about a question is a key part of the skill we are learning here.

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) moles of Zn (mol) What I know now What I have been asked for What I can immediately work out Info moles of H 2 (mol) mole ratio of Zn : H 2 A r of Zn = 65.4 Click on the correct item of info to move it to the “What I have been asked for” box, then click Next. Volume of H 2 = 1.53 dm 3 Mass of impure zinc = 5.84 g Percentage purity Next

What I have been asked for feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back The question asks you to calculate the percentage purity of the zinc. It is important to remember what you have been asked for as this will determine what you work out as the steps towards this.

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) moles of Zn (mol) What I know now What I have been asked for What I can immediately work out Info moles of H 2 (mol) mole ratio of Zn : H 2 A r of Zn = 65.4 Click on the correct item of info to move it to the “What I have been asked for” box, then click Next. Next Volume of H 2 = 1.53 dm 3 Mass of impure zinc = 5.84 g Percentage purity

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) moles of Zn (mol) What I know now ? What I have been asked for ? What I can immediately work out Info Percentage purity moles of H 2 (mol) mole ratio of Zn : H 2 A r of Zn = 65.4 Click on the correct item of info to move it to the "What I can immediately work out” box. Volume of H 2 = 1.53 dm 3 Mass of impure zinc = 5.84 g

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) moles of Zn (mol) What I know now ? What I have been asked for ? What I can immediately work out Info Percentage purity mole ratio of Zn : H 2 A r of Zn = 65.4 Well done. Now select the correct calculation to calculate the number of moles of hydrogen. Volume of H 2 = 1.53 dm 3 Mass of impure zinc = 5.84 g Calculation 1.53 / / 24 2 / / 2 moles of H 2 (mol)

Mole ratio feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back Let’s work out the mole ratio when we are ready to use it.

Percentage purity feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You do not have enough info to calculate this yet – you will need to know the mass of pure zinc first.

Mass of pure zinc Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You do not have enough info to calculate this yet – you will need to know the number of moles of pure zinc first.

Moles of pure zinc Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You do not have enough info to calculate this yet – you will need to know the number of moles of hydrogen first.

Calculation feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back Hydrogen is a gas. The question tells us to assume that 1 mole of gas occupies 24 dm 3 under the conditions used, so you need to use the equation: moles = volume (dm 3 ) / 24

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) moles of Zn (mol) What I know now ? What I have been asked for ? What I can immediately work out Info Percentage purity moles of H 2 = mol mole ratio of Zn : H 2 A r of Zn = 65.4 Well done. Now to make room in your working memory, click on the used item to move it to the bin, then select the next item to immediately work out. Volume of H 2 = 1.53 dm 3 Mass of impure zinc = 5.84 g

Used item feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You used the equation: moles = volume (dm 3 ) / 24 So the item you used was the volume of hydrogen.

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) moles of Zn (mol) What I know now ? What I have been asked for ? What I can immediately work out Info Percentage purity moles of H 2 = mol mole ratio of Zn : H 2 A r of Zn = 65.4 Well done. Now to make room in your working memory, click on the used item to move it to the bin, then select the next item to immediately work out. Volume of H 2 = 1.53 dm 3 Mass of impure zinc = 5.84 g Next

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) moles of Zn (mol) What I know now ? What I have been asked for ? What I can immediately work out Info Percentage purity moles of H 2 = mol mole ratio of Zn : H 2 A r of Zn = 65.4 Well done. Now select the correct mole ratio of Zn : H 2. Mass of impure zinc = 5.84 g Mole ratio from the balanced equation Zn + 2HCl  ZnCl 2 + H 2 1 : 2 2 : 1 1 : 1

Mass of pure zinc Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You do not have enough info to calculate this yet – you will need to know the number of moles of pure zinc first.

Percentage purity feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You do not have enough info to calculate this yet – you will need to know the mass of pure zinc first.

Moles of pure zinc Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You do not have enough info to calculate this yet – you will need to know the mole ratio first.

Mole ratio feedback Back The equation is: Zn + 2HCl  ZnCl 2 + H 2 The mole ratio comes from the balancing numbers – so the ratio Zn : HCl : ZnCl 2 : H 2 = 1 : 2 : 1 : 1 From this you can get the H 2 : Zn mole ratio.

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) moles of Zn (mol) What I know now ? What I have been asked for ? What I can immediately work out Info Percentage purity moles of H 2 = mol mole ratio of Zn : H 2 1 : 1 A r of Zn = 65.4 Well done. Now select the correct item to immediately work out. Mass of impure zinc = 5.84 g

Mass of pure zinc Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You do not have enough info to calculate this yet – you will need to know the number of moles of pure zinc first.

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) What I know now ? What I have been asked for ? What I can immediately work out Info Percentage purity moles of H 2 (mol) = mole ratio of Zn : H 2 1 : 1 A r of Zn = 65.4 Well done. Now select the correct calculation for the number of moles of zinc. Mass of impure zinc = 5.84 g moles of Zn (mol) Calculation 5.84 / / x 1

Moles of pure zinc calculation Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back Since the mass we have is of the impure zinc you cannot use moles = mass / M r to calculate the number of moles. You need to use the number of moles of hydrogen and the mole ratio.

moles of H 2 = mol mole ratio of Zn : H 2 1 : 1 What I know now Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) What I have been asked for ? What I can immediately work out Info Percentage purity A r of Zn = 65.4 Well done. Now select the group items of information that you have used, to be moved to the bin to make room for the latest information, then select what to immediately work out. Mass of impure zinc = 5.84 g moles of Zn = mol

Used item feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You used the number of moles of hydrogen and the mole ratio.

moles of H 2 = mol mole ratio of Zn : H 2 1 : 1 A r of Zn = 65.4Mass of impure zinc = 5.84 g What I know now Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). Mass of pure zinc (g) What I have been asked for ? What I can immediately work out Info Percentage purity Well done. Now select the group items of information that you have used, to be moved to the bin to make room for the latest information, then select what to immediately work out. moles of Zn = mol

Percentage purity feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You do not have enough info to calculate this yet – you will need to know the mass of pure zinc first.

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). What I know now ? What I have been asked for ? What I can immediately work out Info Percentage purity A r of Zn = 65.4 Well done. Now select the correct calculation to work out the mass of pure zinc. Mass of impure zinc = 5.84 g moles of Zn = mol Mass of pure zinc (g) Calculation 5.84 / / x 65.4

Mass of pure zinc calculation Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back Since the mass we have is of the impure zinc you cannot use moles = mass / M r to calculate the number of moles. You need to use the number of moles of zinc and the molar mass of zinc. mass = moles x A r

What I know now ? A r of Zn = 65.4 Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). What I have been asked for ? What I can immediately work out Info Percentage purity Well done. Now select the item or group of items of information that you have used, to be moved to the bin to make room for the latest information, then select what to immediately work out. Mass of impure zinc = 5.84 g moles of Zn = mol Mass of pure zinc = 3.98 g

Used item feedback Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back You used the number of moles of zinc and its relative atomic mass.

What I know now ? Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). What I have been asked for ? What I can immediately work out Info Percentage purity A r of Zn = 65.4 Well done. Now select the item or group of items of information that you have used, to be moved to the bin to make room for the latest information, then select what to immediately work out. Mass of impure zinc = 5.84 g moles of Zn = mol Mass of pure zinc = 3.98 g

Q2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc (assume 1 mole of gas occupies 24 dm 3 under the conditions used for the reaction). What I know now ? What I have been asked for What I can immediately work out Info Well done. Now select the calculation for percentage purity. Mass of impure zinc = 5.84 g Mass of pure zinc = 3.98 g Calculation (5.84 / 3.98) x / 3.98 (3.98 / 5.84) x / 5.84 Percentage purity

Percentage purity of zinc calculation Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Back The equation you need to use is % purity = mass of pure zinc x mass of impure zinc

Percentage purity of zinc calculation Question 2. An impure sample of zinc powder with a mass of 5.84 g was reacted with hydrochloric acid until the reaction was complete. The hydrogen gas produced had a volume of 1.53 dm 3. Calculate the percentage purity of the zinc. (assume 1 mol of gas occupies 24 dm 3 under the conditions used for the reaction) Next Well done. You have completed this question by keeping track of what you know and what you could immediately work out from what you know. The percentage purity was 68.2%. %

Knowing what you know and don’t know End You have now finished the knowing what you know and don’t know skill. There are two other skills to learn: Tabulating the information Storyboarding