Solutions and Concentration - SS1 Chemistry Past Questions and Answers - page 4
What is the molality of a solution if 120 grams of glucose (C6H12O6) is dissolved in 500 grams of water?
Step 1: Convert the given mass of glucose to moles.
Molar mass of glucose (C6H12O6)
= (6 x 12.01 g/mol) + (12 x 1.01 g/mol) + (6 x 16.00 g/mol)
= 180.18 g/mol
Number of moles of glucose = Mass of glucose / Molar mass of glucose
= 120 g / 180.18 g/mol
≈ 0.666 mol
Step 2: Convert the given mass of water to kilograms.
Mass of water = 500 g = 500/1000 kg = 0.5 kg
Step 3: Calculate molality using the formula:
Molality (m) = Number of moles of solute / Mass of solvent (in kg)
= 0.666 mol / 0.5 kg
= 1.332 m
The molality of the solution is 1.332 m.
A solution contains 30 grams of ethanol (C2H5OH) in 70 grams of water. What is the mass percentage of ethanol in the solution?
Step 1: Calculate the total mass of the solution.
Total mass of the solution = Mass of ethanol + Mass of water
= 30 g + 70 g = 100 g
Step 2: Calculate the mass percentage using the formula:
Mass percentage = (Mass of solute / Total mass of solution) x 100
= (30 g / 100 g) x 100
= 30%
The mass percentage of ethanol in the solution is 30%.
A scientist wants to prepare 200 mL of a 0.5 M solution of sodium chloride (NaCl) from a stock solution of 2 M NaCl. How much stock solution should be added to the water to make the desired solution?
50 mL
100 mL
150 mL
200 mL
A pharmacist needs to prepare 500 mL of a 10% (w/v) solution of glucose. How much glucose should be dissolved in water to make the desired solution?
0.5 g
10 g
50 g
100 g
0.5 g
In a w/v (weight/volume) solution, the weight of the solute (glucose) is expressed in grams, and the volume of the solution is expressed in millilitres (mL).
Given:
Volume of the solution (V2) = 500 mL
Concentration of the solution (C2) = 10% (w/v)
Weight of the solute (glucose) = ?
To find the weight of glucose, we need to convert the percentage to a decimal. 10% = 10/100 = 0.1.
Weight of glucose = (Concentration × Volume) / 100
Weight of glucose = (0.1 × 500 mL) / 100
Weight of glucose = 0.5 g
A biologist has a 1 M solution of potassium hydroxide (KOH) and wants to prepare 250 mL of a 0.4 M KOH solution. How much water should be added to the stock solution?
62.5 mL
125 mL
150 mL
375 mL
150 mL
Using the dilution formula, we can calculate the volume of water (V2) to be added to the stock solution.
Given:
C1 (stock solution concentration) = 1 M
V1 (stock solution volume) = ?
C2 (diluted solution concentration) = 0.4 M
V2 (diluted solution volume) = 250 mL
Rearranging the dilution formula, we get:
V1 = (C2 × V2) / C1
Plugging in the values:
V1 = (0.4 M × 250 mL) / 1 M
V1 = 100 mL
To find the volume of water, subtract the stock solution volume from the desired diluted solution volume:
Volume of water = V2 - V1
Volume of water = 250 mL - 100 mL
Volume of water = 150 mL
You have a stock solution of hydrochloric acid (HCl) with a concentration of 10 M. How would you prepare 500 mL of a 2 M HCl solution through dilution?
To calculate the volume of the stock solution needed, we can use the dilution equation:
C1V1 = C2V2
Where:
C1 = initial concentration (10 M)
V1 = initial volume (unknown)
C2 = final concentration (2 M)
V2 = final volume (500 mL)
Rearranging the equation, we have:
V1 = (C2V2) / C1
V1 = (2 M x 500 mL) / 10 M
V1 = 100 mL
Therefore, you would measure 100 mL of the 10 M HCl stock solution and then add enough solvent (typically water) to make the total volume 500 mL.
You need to prepare 250 mL of a 0.5 M sodium hydroxide (NaOH) solution from a stock solution of 2 M NaOH. How would you perform this dilution?
Using the same dilution equation:
C1V1 = C2V2
Where:
C1 = initial concentration (2 M)
V1 = initial volume (unknown)
C2 = final concentration (0.5 M)
V2 = final volume (250 mL)
Rearranging the equation, we have:
V1 = (C2V2) / C1
V1 = (0.5 M x 250 mL) / 2 M
V1 = 62.5 mL
To prepare the 0.5 M NaOH solution, you would measure 62.5 mL of the 2 M NaOH stock solution and then add enough solvent to make the total volume 250 mL.
Question:
You have a 1 L solution of glucose with a concentration of 0.4 M. How would you prepare 500 mL of a 0.1 M glucose solution through dilution?
Answer:
Using the dilution equation:
C1V1 = C2V2
Where:
C1 = initial concentration (0.4 M)
V1 = initial volume (1 L or 1000 mL)
C2 = final concentration (0.1 M)
V2 = final volume (500 mL)
Rearranging the equation, we have:
V1 = (C2V2) / C1
V1 = (0.1 M x 500 mL) / 0.4 M
V1 = 125 mL
To prepare the 0.1 M glucose solution, you would measure 125 mL of the 0.4 M glucose solution and then add enough solvent to make the total volume 500 mL.