Solutions

To fertilise her balcony plants, Nora dissolves $30\ \text{g}$ of soluble fertilizer in water to make $2\ \text{L}$ of solution. Mass concentration is calculated by dividing the grams of solute by the litres of solution. What is the concentration of the fertilizer, in $\text{g/L}$?

To gargle, Marcos dissolves $5\ \text{g}$ of salt in $95\ \text{g}$ of water.

1. a) How many grams of solution does he obtain in total?
2. b) Percentage by mass is calculated by dividing the mass of solute by the total mass of solution and multiplying by $100$. What is the percentage by mass of salt?

A homemade hand sanitiser gel is prepared by mixing $30\ \text{mL}$ of alcohol with aloe vera to make up $150\ \text{mL}$ of gel. Percentage by volume is calculated by dividing the volume of solute by the total volume of solution and multiplying by $100$. What is the percentage by volume of alcohol in the gel?

In the laboratory, Aitana dissolves $12\ \text{g}$ of potassium nitrate in water to make $300\ \text{mL}$ of solution. Calculate the concentration in $\text{g/L}$. Note: convert the volume to litres first.

You are asked to prepare $500\ \text{mL}$ of a copper sulphate solution with a concentration of $8\ \text{g/L}$.

1. a) How many grams of copper sulphate should you weigh out?
2. b) Describe how you would prepare the solution in the laboratory, naming the apparatus you would use (balance, beaker, funnel, $500\ \text{mL}$ volumetric flask...) and at what point you top up to the mark.

A surface disinfectant label states "$70\ \%$ alcohol by volume". How many millilitres of alcohol does a $250\ \text{mL}$ bottle of this disinfectant contain?

A laboratory purchases a stock solution of a reagent with a concentration of $60\ \text{g/L}$. For a lab practical, you need $500\ \text{mL}$ of a diluted solution of $12\ \text{g/L}$.

1. a) What volume of the stock solution must you measure?
2. b) Describe the entire procedure in the laboratory: what equipment you use (pipette or graduated cylinder, $500\ \text{mL}$ volumetric flask, dropper…) and what bringing to the mark means.
3. c) Why is it not enough to just measure the calculated volume of stock solution and add the rest of the water measured with a graduated cylinder to reach $500\ \text{mL}$?

To clean silver, Julia prepares a solution with $40\ \text{g}$ of sodium hydrogen carbonate in $360\ \text{g}$ of water.

1. a) What total mass of solution does she obtain?
2. b) Calculate its percentage by mass of bicarbonate.

You mix $200\ \text{mL}$ of a $30\ \text{g/L}$ salt solution with $300\ \text{mL}$ of another salt solution at $10\ \text{g/L}$ in the same container. Assume the final volume is the sum of the two. The diagram shows the mixture.

1. a) How many grams of salt does each solution provide?
2. b) What is the concentration of the mixture, in $\text{g/L}$?
3. c) Why is the final concentration not $20\ \text{g/L}$, the mean of the two concentrations?

For a crystallisation experiment, you must prepare $400\ \text{g}$ of a $8\ \%$ by mass potassium nitrate solution.

1. a) How many grams of potassium nitrate and how many grams of water should you weigh?
2. b) Describe how you would prepare the solution and explain why this time you do not need a volumetric flask or to top up to the mark.
3. c) Then you add $100\ \text{g}$ more of water. What is the new percentage by mass?