Watered Dilutions LAB

The first square shows a tiny volume of 0.010 M HCl. Sketch what you expect to see in the same tiny volume when you dilute with water as indicated. Calculate the molarity and the pH of the two new solutions.

How many drops of the 0.010 M HCl solution would you need in order to have the same number of hydrogen ions as in one drop of 0.10 M HCl?

• 20
• 10
• 15
• 5

Predict the pH for three successive dilutions of 0.010 M HCl as indicated in the table. For each successive dilution, 9 mL of water is added to 1 mL of solution.

Suppose you have 0.010 M sodium hydroxide, NaOH, with a pH of 12. Predict the pH if you add 9 mL of water to 1 mL of 0.010 M NaOH.

• pH 11

• pH 12

• pH 13

• pH 14

Answer explanation

The OH^– concentration becomes 1 x 10^–3 M, making the H⁺ concentration 1 x 10^–11 M. So, the pH is 11.

How much would you have to dilute 0.010 M NaOH to get a pH of 10?

• You have to dilute 1 mL of solution to 100 mL

• You have to dilute 1 mL of solution to 10 mL

• You have to dilute 1 mL of solution to 1000 mL

If you came up with an experiment in order see if you could get Solution 4 to obtain a pH greater than 7 what dilution, what would you conclude?

• Add more acidic substance to Solution 4.
• Increase the temperature of Solution 4.
• Dilute Solution 4 with a basic substance.
• You cannot change the nature of a solution via dilution.

What happens to the pH of an acid or basic solution when it is diluted with water?

• The pH increases

• The pH decreases

• The pH approaches 7

• The pH increases past 7

Answer explanation

The pH approaches 7. This is the pH of pure water. As more and more water is added, the acid or base spreads out into a larger and larger volume until the number of moles per liter equals 1 x10^–7

As we dilute a solution.....

• The volume increases and the molarity (M) increases

• The volume increases and the molarity (M) decreases

• The volume decreases and the molarity (M) increases

• The volume decreases and the molarity (M) decreases

How many mL of stock solution of 2M HCl do you need to prepare 100 mL of 0.150M HCl?

• 7.5 mL

• 15 mL

• 1333 mL

• 200 mL

What does it mean to dilute a solution?

• lower the concentration of solute per solvent

• increase the concentration of solute per solvent

Answer explanation

Diluting a solution means to decrease the concentration of solute in the solvent. This is achieved by adding more solvent to the solution, which lowers the concentration of the solute. Therefore, the correct answer to the question is 'lower the concentration of solute per solvent'.