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Gcse Chemistry > Chemical Analysis > Flashcards

Chemical Analysis Flashcards

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1
Q

What is the difference between a pure and impure substance?

A

Pure- contains only one element
Impure- contains a mixture of elements

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2
Q

Compare the difference between pure and impure substances regarding melting/boiling points-

A

Pure substances-
Sharp melting and boiling points
Boil at lower temperatures
Melts at higher temperatures

Impure substances-
Melting/boiling points are not sharp
Boils at a higher temperature
Melts at a lower temperature

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3
Q

Which two substances are mixtures?
Air
Graphite
Carbon dioxide
Graphite
Sodium chloride
Steel

A

Steel ( is a form of an alloy which is a mixture of elements)
Air ( mixture of nitrogen, oxygen, carbon which are not chemically bonded together)

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4
Q

Give 3 types of alloys-

A

Steel

Bronze

Brass

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5
Q

Why are Separation techniques are
used to separate the
mixtures and not
compounds?

A

Mixtures do not contain chemical bonding between atoms of different substances.
But compounds contain chemical bonding between atoms of different elements.

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6
Q

Sulfur is soluble in the flammable liquid xylene but not in
water. Sodium nitrate is soluble in water but not in xylene.
Describe two ways to separate a mixture of sulfur powder
and sodium nitrate to collect pure samples of each liquid.

A

Add water, stir and filter the solution.
Sulfur residue on the filter paper, wait for it to dry.
Evaporate the water from the filtrate sodium nitrate with a water bath until the point of crystallization.

Add xylene, stir and filter the solution.
Sodium nitrate residue on the filter paper, wait for it to dry.
Evaporate the xylene from the filtrate sulfur with a water bath until the point of crystallization.

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7
Q

How do we find the RF value?

A

By dividing the distance traveled by the substance (colored dot) / distance traveled by the solvent

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8
Q

Write all the tests of common gases and results for a positive reaction-

A

Hydrogen:
Test- lighted splint
Result- makes a pop sound

Oxygen:
Test- glowing splint
Result- relights

Ammonia:
Test- sodium hydroxide
Result- gas produced turns damp red litmus into blue

Carbon dioxide:
Test- hydrochloric acid
Result- turns cloudy white

Chlorine:
Test- Litmus paper
Result- makes damp blue litmus turn into red and then bleaches it white

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9
Q

What is the stationary phase and mobile phase in chromatography?

A

Stationary phase- The paper
Mobile phase- Solvent

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10
Q

What will happen if ink is used instead of pencil on the baseline of chromatography paper?

A

Ink will get dissolved in the solvent/ wash off in the paper

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11
Q

How do you determine if other food colorings are the same composition as the food coloring you are testing?

A

If they’re on the same alignment. (The same horizontal line)

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12
Q

What will happen if spots are under
solvent?

A

Dissolved in the solvent

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13
Q

Why is the baseline drawn in pencil?

A

Pencil will not move in the solvent

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14
Q

Describe how to do a flame test on a solution containing a metal ion-

A

Heat the wire
Dip the wire in the salt to be tested
Dip in HCL
Hold the wire at the edge of the blue Bunsen flame and observe what colour it contains.

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15
Q

State all of the flame tests-

A

Lithium- crimson
Sodium hydroxide- yellow
Potassium iodide- lilac
Calcium carbonate- red
Barium chloride- green

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16
Q

A solution contains calcium and lithium ions, suggest one reason why a flame test could not be used to identify the metal ions-

A

Because calcium and lithium produce similar shades of red.

17
Q

Describe some advantages of using instrumental methods compared to chemical tests considering the length of time and amount of chemical used- 2 marker

A

Instrumental methods are faster.
Smaller amount of chemical needs to be used

18
Q

What happens when you add sodium hydroxide to Mg,Al, Ca: relate to their solubility-

A

Mg, ca are insoluble in sodium hydroxide.
Al is soluble in NaOH meaning that if the solution is dissolved, it contains aluminum. If not, then it contains Mg or Ca.

19
Q

Describe the two further tests the student would have to do to show that salt X contains magnesium ions and not aluminum or calcium- 4 marker

A

1- Add excess sodium hydroxide.
2-If the White precipitate remains, then aluminum is not present, so we need to distinguish between magnesium and calcium by 3- carrying out a flame test.
4- If the colour produced were not red/ orange then it is not calcium and is magnesium.

20
Q

The student added sodium hydroxide solution until it was in excess in the salt solution, describe what the student would see if the salt contained calcium ions-

A

White precipitate forms.
Calcium is insoluble in excess sodium hydroxide solution until there will be no further change

21
Q

Why do the results not prove that it is calcium ions? 1 mark What could be an additional test that could prove it is calcium ions? 2 marks

A

It can also contain magnesium ions because same results with magnesium.

Flame test, if red flame is produced, calcium ions are present.

22
Q

What ions form colour we precipitates? And what colours do they form?

A

Copper 2+ : blue precipitate
Iron 2+ : green precipitate
Iron 3+ brown precipitate

23
Q

State and explain the tests for halides, sulfates, carbonates:

A

Test for halides-
Add dilute nitric acid to the solution.
Add a few drop of silver nitrate.
White precipitate- chloride ions formed
Cream precipitate- bromide ions formed
Yellow precipitate- iodide ions formed

Test for sulfates:
Add dilute HCL to the solution.
Add a few drops of barium chloride.
If a white precipitate forms, sulfates ions present.

Test for carbonates-
Add dilute acid to carbonates.
Collect the gas that has given off
Bubble the gas with limewater. And if limewater turns cloudy white then carbon dioxide is the gas. And carbonate ions are present.

24
Q

Describe a test to show that barium chloride contains bromide ions-

A

Add dilute acid to the barium chloride solution. Add a few drops of silver nitrate. Cream precipitate would form if bromide ions are present

Gcse Chemistry (12 decks)

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