Practice questions Module 1. Basic skills M r and moles to grams Grams and moles to M r M r and grams to moles Concentration and volume to moles Concentration.

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Presentation transcript:

Practice questions Module 1

Basic skills M r and moles to grams Grams and moles to M r M r and grams to moles Concentration and volume to moles Concentration and moles to volume Volume and moles to concentration Read equation, use it to calulate moles Gas equation – derive any one value from the others by changing subject and substituting in.

e.g. 1 What will you do? HCl + NaOH  NaCl + H 2 O 500 ml of acid was spilt. 670ml of 1 molar alkali was needed to neutralise it, so what was the concentration of the original acid? Suggested steps: 1.Moles of alkali from volume in dm 3 x concentration 2.Equation shows this equals moles of acid 3.Find concentration from volume and moles 4.If you’re clever you can do it in one go. I don’t.

e.g. 2 What will you do? H 2 SO 4 + 2NaOH  Na 2 SO 4 + H 2 O 180 ml of alkali was spilt. 275ml of 0.25 molar acid was needed to neutralise it, so what was the concentration of the original alkali? Suggested steps: 1.Moles of acid from concentration x volume (don’t forget this needs to be in dm 3 ) 2.Equation shows this equals half the moles of alkali so double it 3.Find concentration from volume and moles

e.g. 3 What will you do? H 2 SO 4 + Na 2 CO 3  Na 2 SO 4 + H 2 O + CO 2 210g of sodium carbonate was reacted with an excess of 0.5 molar acid. What volume of carbon dioxide was evolved (assume 298K and 101kPa, R=8.31)? Likely steps: 1.Moles of carbonate from mass and M r 2.Equation shows this equals the moles of CO 2 3.Could use 24 litres per mol or use ideal gas equation 4.Change subject of ideal gas equation 5.Use IG equation to find volume of this many moles of gas.

e.g. 4 What will you do? H 2 SO 4 + 2NaHCO 3  Na 2 SO 4 + 2H 2 O + 2CO g of sodium hydrogencarbonate was reacted with an excess of acid. What volume of carbon dioxide was evolved? Likely steps: 1.Moles of carbonate from mass and M r 2.Equation shows this equals the moles of CO 2 3.Multiply moles by 24 dm 3 to find volume of this many moles of gas.

e.g. 5 What will you do? 2H 2 (g) + O 2 (g)  2H 2 O (g) 1.2 dm 3 of hydrogen was placed in a balloon at 110kPa and 293K and ignited. What mass of water vapour was produced? 1.Moles of hydrogen from ideal gas equation 2.Equation shows this equals the moles of H 2 O 3.Find mass of this many moles of gas.

e.g. 6 What will you do? Some sucrose (C 6 H 12 O 6 ) is burnt in a school laboratory. Write a full balanced equation for this C 6 H 12 O 6 (s) + 6O 2 (g)  6H 2 O(g) + 6CO 2 (g) The mass of the sucrose was 14.3g. What volume of carbon dioxide was evolved? 1.Moles of sucrose from mass and M r 2.Equation shows the moles of CO 2 are 6 times this, so multiply by 6 3.Assume normal temperature and pressure – 100kPa, 298K. (or could use 24 litres per mole) 4.Use ideal gas equation to find the volume of this many moles of gas.

e.g. 7 What will you do? Some propanol (C 3 H 7 OH) is burnt in a school laboratory. Write a full balanced equation for this 2C 3 H 7 OH (l) + 9O 2 (g)  8H 2 O(g) + 6CO 2 (g) The mass of the propanol was 119g. What mass of carbon dioxide was evolved? 1.Moles of propanol from mass and M r 2.Equation shows the moles of CO 2 are 3 times this, so multiply by 3 3.Find the mass of this many moles of gas.

e.g. 8 What will you do?