1. Calculating Concentration How do we measure concentration? How do we compare concentrations?

2. The Big Idea… Concentrations of solutions are expressed as fractions using the amount of solute over the amount of solvent ( )… We can change the concentration of a solution by changing the amount of solute and/or solvent Solute g Solvent ml

3. Textbook Reading Please read pages 24, 25, & 28 in the Science in Action 8 Textbook

4. Concentration If we are given a concentrated substance, we are saying that we have a large amount of solute particles in a given amount of solvent particles If we are given a diluted substance, we are saying that we have a small amount of solute particles in a given amount of solvent particles Think of making orange juice or iced tea as an analogy

5. Concentration Concentration is a term that refers to the measurement of the amount of solute per unit of solvent We measure concentration in g / ml We can also measure it in % We can create solutions with specific concentrations

6. Example Here we have a 200 ml flask full of water… we add 50 g of salt to the water What is the concentration of the salt water solution in the box? 50 g 200 ml Therefore, the salt water concentration is 50 g / 200 ml

7. Concentration Examples of measuring concentration: If we have 20 g of solute in 100 ml of solvent… the concentration is said to be: 20 g / 100 ml If we have 125 g of solute in 500 ml of solvent… the concentration is said to be: 125 g / 500 ml

8. Setting up the Fraction How to set up concentrating fractions: 1. Put the value for the solute (g) in the numerators position 2. Put the value for the solvent (ml) in the denominators position 3. If we have 125 g of solute in 500 ml of solvent… We write that as follows 125 g 500 ml

9. Example Questions 1) How would you write out the concentration fraction if you have 450 ml of water and 61 g of koolaid dissolved in it? Concentration = 2) What is the concentration fraction if you have 353 g of baking soda dissolved in 3200 ml of water? Concentration = 61 g 450 ml 353 g 3200 ml

10. Example Questions 3) How would you write out the concentration fraction if you have 250 ml of milk and 84 g of chocolate mix dissolved in it? Concentration = 4) What is the concentration fraction if you have 77 g of sugar dissolved in 600 ml of water? Concentration = 84 g 250 ml 77 g 600 ml

11. Equal Concentrations We can write Equivalent concentrations by multiplying or dividing both the numerator and the denominator by the same number Example We are given a recipe for ice tea that calls for a concentration of 30 g / 200 ml but we need 10 x more iced tea for 10 x more people to drink. However, it must have the same concentration. What is an equivalent concentration value 30 g 200 ml x 10 300 g x 10 2000 ml

12. Example Questions 1) What is one different but equal concentration fraction if you have 25 g of sugar dissolved in 300ml of water but you want to triple the amount? Start by writing down your original concentration 2) What is one different but equal concentration fraction if you have 400 ml of water and 30 g of sugar dissolved in that water but want to double the amount ? Start by writing down your original concentration

13. Example Questions 3) What are two different but equal concentration fractions if you have 25 g of sugar dissolved in 75 ml of water? Start by writing down your original concentration 4) What are two different but equal concentration fractions if you have 150 ml of water and 20 g of sugar dissolved in that water? Start by writing down your original concentration

14. Different Concentrations We can write different concentrations by changing one of the two numbers in the fraction Example We have an ice tea concentration of 15 g / 300 ml and want to write a new value so that we have a higher concentration (stronger ice tea) We can either write a value with a higher numerator (solute value) 25 g Or we can write a value with a lower denominator (solvent value) 175 ml

15. Different Concentrations Demo Time !!!

16. Example Questions 1) How would you write out a concentration that is stronger than 20 g of iced tea dissolved in 350 ml of water? Note… there are two ways! 2) How would you write out a concentration that is weaker than 20 g of iced tea dissolved in 350 ml of water? Note… there are two ways!

17. Example Questions 1) How would you write out a concentration that is stronger than 35 g of iced tea dissolved in 200 ml of water? Note… there are two ways! 2) How would you write out a concentration that is weaker than 35 g of iced tea dissolved in 200 ml of water? Note… there are two ways!

18. Comparing Concentrations In order to compare concentrations, you must have a common volume from which to make the comparison This is similar to finding a common denominator when working with fractions in math Look at this example: Which has the strongest concentration? 20 g 700 g 3 g 85 g 50 ml 1500 ml 10 ml 500 ml

19. Comparing Concentrations STEP 1 Find a common denominator for the group 20 g 700 g 3 g 85 g 50 ml 1500 ml 10 ml 500 ml Each volume will divide into 1500 ml, therefore that can be our common denominator 50 ml x 30 = 1500 ml 1500 ml x 1 = 1500 ml 10 ml x 150 = 1500 ml 500 ml x 3 = 1500 ml

20. Comparing Concentrations Step 2 Now multiply the amount of solute by the same number you multiplied the volume by to get 1500 20 g 700 g 3 g 85 g 50 ml 1500 ml 10 ml 500 ml 20 g x 30 = 600 g 700 g x 1 = 700 g 3 g x 150 = 450 g 85 g x 3 = 255 g

21. Comparing Concentrations STEP 3 Rewrite the concentration as measurements / 1500 ml so that they can all be compared on a level playing field 600 g 700 g 450 g 255 g 1500 ml 1500 ml 1500 ml 1500 ml We can see now that 700 g is the most out of the four… therefore the 700 g / 1500 ml has the highest concentration out of all four 85 g / 500 ml was the most diluted solution out of all four

22. Lets Practice! Here are four more concentration, figure out which one has the highest concentration, and which one is the most diluted? 10 g 30 g 45 g 85 g 25 ml 100 ml 75 ml 300 ml Step 1 - Find a common denominator for all four Step 2 - Multiply the numerator by the factor Step 3 - Rewrite each concentration to compare

23. Lets Practice! 10 g 30 g 45 g 85 g 25 ml 100 ml 75 ml 300 ml x 12 x 3 x 4 x 1 120 g 90 g 180 g 85 g 300 ml 300 ml 300 ml 300 ml Now all of the values are expressed in terms of /300 ml so thy can be compared on an even playing field !

24. Changing to 100 ml Change these concentration values so that they are given in terms of __ g / 100 ml 10 g 30 g 120 g 80 g 25 ml 100 ml 500 ml 200 ml The common denominator for all four must be 100 Multiply or divide the numerator by the factor Rewrite each concentration to compare

25. Changing to 100 ml 10 g 30 g 120 g 80 g 25 ml 100 ml 500 ml 200 ml x 4 x 1 ÷ 5 ÷ 2 40 g 30 g 24 g 40 g 100 ml 100 ml 100 ml 100 ml Now all of the concentration values are expressed in 100 ml volumes as asked… full marks!

26. Home work! You are being given a work sheet to practice this concept on Please try to tackle all of the questions on it and make sure that understand how to compare concentrations because it will be on the up coming lab report, as well as any quizzes