Acids

Question 1

What are the common acids you need to know?

Answer 1

HCl, H2SO4,
HNO3 and CH3COOH

Question 2

What are the common alkali you need to know?

Answer 2

NaOH, KOH and NH3

Question 3

What do acids release into solution?

Answer 3

H+
In ethanoic acid it comes from the COOH (CH3C00H)

Question 4

What do alkali release into solution>

Answer 4

OH-
Ammonia doesn’t contain a hydroxide but when in water it reacts.
NH3 + H20 = NH4+ + OH-

Question 5

What is the difference between weak and strong acids and give an example of a weak acid.

Answer 5

Weak acids partially dissociate and strong acids fully dissociate. Weak acids are carboxylic acids like ethanoic acid (CH3C00H). It forms ethanoate (CH3COO-) and H+

Question 6

What are strong and weak alkali and what is an example of a weak alkali?

Answer 6

Strong = fully dissociate, weak = partially dissociate.
An example of a weak alkali is NH3

Question 7

What is a neutralisation reaction?

Answer 7

H+ + OH- = H20

Question 8

How do acids react with ammonia?

Answer 8

It makes an ammonium salt, NO WATER.
eg: HCl + NH3 = NH4Cl

Question 9

How do you make a standard solution for a tritration?

Answer 9

First find out how many moles will be present in the concentration and volume of the solid. (n=cv)
That no. moles needs to go into the volumetric flask, so the mass of this solid is needed. (nxMr).
That mass (measured in a weighing boat on a scale) is added into a beaker, dissolved with distilled water then poured into a volumetric mask with a funnel. Everything is washed (beaker, funnel, glass rod) into the flask to get all the solute. Then add distilled water to the scratch mark (when near it use glass pipette). The bottom of the meniscus should touch this - read at eye level. Invert flask to make sure its fully mixed and sissolved. Now you have your standard solution which is the specified volume and concentration.

Question 10

What are tritrations used for?

Answer 10

To find the concentrations of an acid or alkali.

Question 11

What goes in the burette?

Answer 11

An acid or alkali of KNOWN concentration

Question 12

What goes in the conical flask?

Answer 12

An acid or alkali of an UNKNOWN concentration

Question 13

What is the end point of a tritration?

Answer 13

Where the indicator changes colour and the acid and alkali have fully reacted.

Question 14

How long should you repeat the tritration for?

Answer 14

Until 2 results are concordant (within 0.1cm3 of each other. Then take an average.

Question 15

What indicators can you use for a tritration and what are the colour changes?

Answer 15

Phenolphalien - acid=colourless, alkali=pink
Methyl Orange - acid yellow, alkali=orange

Question 16

What is a standard solution?

Answer 16

A solution of known concentration

Question 17

Why is distilled water used for standard solutions?

Answer 17

It is deionsied so there are no ions that can react with the solid, altering the concentration of the standard solution. If inaccurate the tritration will no longer work.

Question 18

What is the formula for percentage uncertainty?

Answer 18

% uncertainty = uncertainty/measured value x 100
If taking two readings:
uncertainty x 2/measured value

Question 19

If the uncertainty is not listed on the equipment how do you find it?

Answer 19

Assume that it is +/- half the smallest measurement on the scale.
eg: the thermometer’s smallest measurement is 0.1 celcius so the uncertainty is +/- 0.05

Question 20

What is percentage uncertainty?

Answer 20

The uncertainty of a measurement compared to the value of the measuement.

Question 21

When does percentage uncertainty double?

Answer 21

Depends on how many times we are taking a reading from a=equipment.
Thermometer, measuring cylinder or balance = one reading = one consideration of uncertainty.
Change in temperature, burette or mass change = 2 readings = double the uncertainty.