Preparation Of Solutions

Question 1

Calculate the concentration of a stock solution with a specific gravity of 2.5g/cm3, a percentage purity of 52%, and a molar mass of 40gmol-1.

Answer 1

32.5 moldm-3

Question 2

How do you convert a concentration of 0.05% (w/v) NaCl solution to ppm?

Answer 2

Multiply the percentage concentration (0.05%) by 106. The result is 500ppm.

Question 3

Define parts per million (ppm) and how it is calculated.

Answer 3

PPM is a unit of concentration that expresses the ratio of a solute’s weight or volume to the weight or volume of the solution. To calculate ppm, multiply the percentage concentration by 106.

Question 4

Describe how to prepare a 0.1moldm-3 HCl solution from a stock solution of concentration 11moldm-3.

Answer 4

Transfer 9.09cm3 of the 11moldm-3 HCl solution into a known volumetric flask containing distilled water, shake well to dissolve, and then top it up to the specified mark with distilled water.

Question 5

Describe the steps involved in preparing a 1000cm3 solution with an amount concentration of 0.25 moldm-3.

Answer 5

1. Calculate the mass of the solute needed using the formula m = C x M x V. 2. Weigh the calculated mass of the solute in a clean dry beaker using an electronic balance. 3. Add distilled water to the beaker and stir to dissolve the solute. 4. Transfer the resulting solution to a 1000cm3 volumetric flask using a funnel and stirring rod. 5. Wash the beaker and stirring rod, transferring all washings back to the volumetric flask. 6. Add distilled water carefully to the flask until the total volume reaches the 1000cm3 mark. Cork and label the solution if necessary.

Question 6

Describe the steps involved in preparing a 250cm3 solution of Na2CO3 at a concentration of 0.50 moldm-3.

Answer 6

1. Calculate the volume of the stock solution needed using the dilution formula CiVi = CfVf. 2. Use a burette or pipette to transfer the calculated volume of the stock solution into a known volumetric flask containing distilled water. 3. Shake the flask well to dissolve the solution. 4. Top up the flask to the specified mark

Question 7

Describe the steps involved in preparing a 500cm3 solution of Na2CO3 at a concentration of 2moldm3.

Answer 7

1. Weigh 106g of Na2CO3 in a clean dry beaker using an electronic balance. Add distilled water and stir to dissolve the solute. 2. Transfer the resulting solution to a 500cm3 volumetric flask using a funnel and stirring rod. 3. Wash the beaker and stirring rod, transferring allings back to the volumetric flask. 4. Add distilled water carefully to the flask until the total volume reaches the500cm3 mark. Cork and label the solution if necessary

Question 8

What is the dilution factor?

Answer 8

It is the number of times the volume of a concentrated solution is diluted to obtain a less concentrated solution.

Question 9

Describe the process of dilution.

Answer 9

It is the process of adding distilled water to a concentrated standard solution to obtain a solution of lower concentration.

Question 10

Describe a standard solution.

Answer 10

A standard solution is a solution whose concentration is accurately known.

Question 11

What are the steps involved in calculating the concentration of a stock solution?

Answer 11

Calculate the pure mass of the substance, calculate the number of moles of the pure solute, and then calculate the concentration of the solution.

Question 12

Define stock solution.

Answer 12

It is a highly concentrated solution with an accurately known concentration that can be diluted for use in the lab.

Question 13

What is an assay?

Answer 13

It is a full list of the experimentally determined purity of a compound including its impurities.

Question 14

Describe the properties of KOH and NaOH when dissolved in distilled water.

Answer 14

They do not dissolve in distilled water.

Question 15

List two properties of a primary standard.

Answer 15

1. It should be easily purified / must be available in a very pure state. 2. It must have a relatively high molecular mass to minimize the effects of weighing errors.

Question 16

What is a primary standard?

Answer 16

A primary standard is a substance that can be easily purified and used to prepare a standard solution.

Question 17

Define a secondary standard.

Answer 17

A secondary standard is a compound whose concentration is measured by titration with a primary standard.

Question 18

What is the purpose of a primary standard?

Answer 18

The purpose of a primary standard is to serve as a highly pure substance that can be used to prepare a standard solution

Question 19

Describe the properties of a primary standard.

Answer 19

A primary standard must be available in a highly pure state, have a relatively high molecular mass, not change in weight while being weighed, react speedily and completely with the substance to be standardized, be inexpensive, and not decompose on heating.