Chemical Analysis

Question 1

What is a formulation

Answer 1

Formulations are useful mixtures with a precise purpose that are made by following a formula

Question 2

What can impurities in a substance do

Answer 2

It will lower the melting point and increase the meting range of a substance

Impurities may also increase the boiling point and may result in a sample boiling at a range of temperatures

Question 3

How can boiling/melting point determine purity

Answer 3

Pure substances only boil/melt at certain temps

You can test this out by comparing the melt/boiling point of two substances. The closer the measured value is to the true value the purer the sample is.

Question 4

What is a pure substance

Answer 4

A pure substance is something that only conatins one compound or element throughout- not mixed with anything else

Question 5

What is chromatography and how does it seperate mixtures

Answer 5

Chromatography can be used to seperate mixtures and can give information to identify substances.

Involves a mobile and stationary phase where seperation depends on the distribution of substances between the phases.

Question 6

Calcuation for Rf value

Answer 6

Distance moved by substance
———————————————– = Rf value
Distance moved by solvent

Question 7

How does chromatography be used to distinguish between pure and impure susbtances

Answer 7

Different compounds have different Rf values in different solvents, which is used to identify compounds. Compounds in a mixture will seperate into different spots in a solvent but a pure compound will produce a single spot in all solvents

Question 8

Required practical: how is paper chromatogaphy used to seperate and tell the difference between coloured substances

Answer 8

1) substances move between mobile and stationary phase (equillibrium formed)

2) components in a mixture will normally seperate through the stationary phase, as the components spend different amount of time in the mobile phase. Number of spots may change in different solvents as distribution changes due to solvent

3)molecules with a higher solubility in the solvent will spend more time in the mobile phase.

4) Pure substances only form one spot (one substance)

Question 9

Test for oxygen

Test for hydrogen

Test for chlorine

Test for carbon dioxide

Answer 9

Oxygen: glowing splint inside a test tube containig oxygen , the oxygen will relight the glowing splint

Hydrogen: Hold a lit splint at the end of a tets tube containing hydrogen if there is a squeaky pop hydrogen is present

Chlorine: Bleaches damp litmus paper turning it white

Carbon dioixde: Bubbling carbon dioxide through an aqueous solution of calcium hydroxide causes solution to turn cloudy