formula, equations and amounts of substances

Question 1

how many particles are in a mole?

Answer 1

there are 6.02x10^23 particles. this is also known as the avagadro constant.

Question 2

how do you work out the number of atoms in something?

Answer 2

first wrk out the amount of moles in the molecule; then multiply that by the avagadro constant; finally multiply that by the number of atoms in 1 molecule.

Question 3

how do you calculate the % composition of an element?

Answer 3

total mass of an element in a compound/total mass of a compound x 100

Question 4

how do you use balanced equations to work out masses?

Answer 4

firstly you need to calculate the moles of the reactant. then use the ratio to work out the moles of the product. and therefore you can work out the mass.

Question 5

what happens in a displacement reaction?

Answer 5

a more reactive element replaces a less reactive one.

Question 6

what experiment can you use to measure the molar volume of gas?

Answer 6

measure out a set volume of HCl into a conical flask connected to a gas syringe.add a known mass of sodium carbonate and allow the reaction to go to completion.
repeat the experiment varying the volume of sodium each time. then work out the moles of the NaCO3 and substitute them into the equation volume / moles

Question 7

how d you use volume calculations?

Answer 7

from the equation for out the ratio of reactants to products (all the moles combined for the products) and then multiply the volume of given gas by the ratio.

Question 8

what is the ideal gas equation, and what do all the components mean

Answer 8

pV=nRT 
p= pressure(Pa)
V= volume(m^3)
n= number of moles
R= the gas constant 8.31 j k-1 mol-1
T= temperature(K)

Question 9

when can you use the ideal gas equation?

Answer 9

to work out the mass of an unknown volatile liquid
put a known mass of the liquid in a flask, then attach it to a gas string, gently warm the apparatus in a water bath until the liquid completely evaporates. record the volume of gas in the syringe and the temp of the water bath. use the ideal gas equation to work out how many moles of liquid were in your sample.

Question 10

what colour does methyl orange go?

Answer 10

yellow in alkali and red in acid.

Question 11

what colour does phenolphthalein go?

Answer 11

pink in alkali and colourless in acid

Question 12

how do you calculate concentrations from titrations?

Answer 12

first write a balanced equation on what you know and what you need to know. work out the moles of the solution that all the information was given for. from there using ratios work out the concentration of the other solution.

Question 13

how do you use titration to work out the concentration of an acid?

Answer 13

first calculate the concentration of the standard solution used; now wright a balanced equation showing what you do know and what you are trying to work out; from their work out the moles of the standard solution (concentration x volume) and use the ratio to then work out the concentration of the acid

Question 14

how do you work out volumes from titration?

Answer 14

same as working out concentration except that you are working out volume.

Question 15

who do you calculate % uncertainty?

Answer 15

percentage uncertainty = uncertainty/reading x100

Question 16

how can you reduce the % uncertainty?

Answer 16

use more precise apparatus

planning - if you use larger amounts using the same measuring apparatus then the % uncertainty will be smaller.

Question 17

what is a systematic error?

Answer 17

systematic errors are the same overtime that you repeat an experiment. they can be accused by the set up or the equipment.

Question 18

what is a random error?

Answer 18

random errors vary - they’re what make the results a but different each time you repeat an experiment.

Question 19

what can you do to get rid of random error?

Answer 19

when you have repeated the results calculate the mean. this however does not get rid of systematic errors.

Question 20

in titrations how do you find the total uncertainty in the final result?

Answer 20

find the percentage uncertainty for each bit of equipment. add the individual percentage uncertainties together. this gives the percentage uncertainty in the final result.
use this to work out the actual uncertainty in the final result.

Question 21

what is the theoretical yield?

Answer 21

the theoretical yield is the mass of the product that should be made in a reaction if no chemicals are lost in the process.

Question 22

what is atom economy?

Answer 22

atom economy is the measure of a proportion of reactant atoms that end uo in the desired product in the balanced equation.

Question 23

how do you calculate atom economy?

Answer 23

molar mass of desired product/sum off molar masses of all products.

Question 24

when is the atom economy alwase 100%

Answer 24

in an addition reaction.