Amount of substance

Question 1

What is the equation involving mass, moles and mr?

Answer 1

mass= moles X mr

Question 2

What is the equation involving moles, conc and vol?

Answer 2

moles= conc X vol

Question 3

What is included in the PV=nRT equation?

Answer 3

Pressure (Pa) X volume (m^3) =

no. of moles X gas constant X temperature (K)

Question 4

How do you convert dm^3 and cm^3 into m^3 ?

Answer 4

cm^3 /1,000,000 = m^3 (divide by 1 million)

dm^3 /1,000 =m^3 (divide by 1 thousand)

Question 5

How do you convert Kpa and Mpa and atm into Pa?

Answer 5

Kpa (X 1,000) = Pa
Mpa (X 1,000,000) = Pa
1atm = 101,000 Pa

Question 6

For concentration, how do you get from mol d^-3 to g dm^-3 ?

Answer 6

You multiply by the mr

mass=molesXmr

Question 7

For temperature, how do you convert degrees celsius into kelvin?

Answer 7

You add 273.

Question 8

What does concordant mean?

Answer 8

It’s a level of accuracy and it means within +/- 0.10cm^3

Question 9

How do you calculate atom economy?

Answer 9

mr of the desired product
/total mr of the reactants
X100 (percentage)

Question 10

What is atom economy?

Answer 10

A measure of what proportion of the products of a reaction are the desired product and how much is waste.

Question 11

Do you need ratio for atom economy?

Answer 11

Yes.

Question 12

Which of percentage yield and atom economy can be changed?

Answer 12

Percentage yield  (e.g. human error)
(Atom economy stays the same.)

Question 13

Do you need ratio for percentage yield ?

Answer 13

Sometimes.

If working out theoretical mass=for ratio of moles

Question 14

Do you need ratio for percentage yield ?

Answer 14

Sometimes.

If working out theoretical mass=for ratio of moles.

Question 15

How do you go from tonnes, kg, or mg to g?

Answer 15

1 ton = 1,000,000g (X1,000,000)
1kg = 1000g (X1,000)
1mg = 0.001g (/1,000)

Question 16

Finding empirical formula and molecular formula of unknown compound

Answer 16

Mr of element/ mr of thing it’s in
X mass
/mr of element
Both/ the smallest

Question 17

Practical steps for finding x for a hydrated sample

Answer 17

1. Weigh empty boiling tube with a balance and record in table.
2. Place about 2cm^3 depth of your hydrated sample and record in table.
3. Heat tube for 1min (using test tube holders).
4. Record the mass of the tube.
5. Repeat steps 3 and 4 until mass remains constant. (if still steam = not constant = more water to still be lost).

Question 18

How to make a standard solution?

Answer 18

1.Add solid to a small beaker & add approx. 50cm^3 of distilled water & stir until fully dissolved.
2.Transfer this into a 250cm^3 volumetric flask using a funnel (no filter=fully dissolved)
3.Rinse beaker with distilled water & add washings
4.Slowly add water until near meniscus
5.Using a dropper add water until the meniscus is level with the line (using eye-level)
6.That is 250cm^3
7.Place stopper on the top & invert 10 times to mix the solution thoroughly
conc=moles/vol(in dm^3) solid=weigh by diff moles=mass/mr

Question 19

How do you weigh by difference?

Answer 19

1.Zero the balance
2.Place the weighing boat on the balance (M1)
3.Add the rough amount of solid to the boat and record its mass (M2)
4.Add the solid mass to a beaker then record the mass of the boat again (M3)
Subtract M2-M3 = exact mass of solid in beaker.

Question 20

Steps for titration (acid added to alkali)

Answer 20

1. Use pipette and pipette filler to add 25cm^3 of sodium hydroxide solution to a clean conical flask
2. Add a few drops of indicator then put the conical flask on a white tile
3. Fill the burette w/ hydrochloric acid & note starting volume
4. Slowly add acid from burette to alkali in the conical flask, swirling to mix
5. Stop adding acid when the end-point is reached (more accurate if added drop by drop near end-point) & note the final volume reading
6. Calculate volume of the acid added to neutralise (titre value)
7. Repeat 1-5 until concordant titres are obtained

Question 21

What does end-point mean?

Answer 21

When the indicator first permanently changes colour.

Question 22

Why rinse the inside of a conical flask during titration? & why doesn’t this affect the accuracy of the titre?

Answer 22

Returns reagent on the sides of the flask to the reaction mixture (to ensure all of the acid/alkali reacts)
Water doesn’t change the number of moles of reagent.