Moles

Question 1

Moles

Answer 1

an amount used in chemistry. a mole of a substance is the amount of that substance that contains 6X10 to the 23 molecules of the substance

Question 2

relative molecular mass

Answer 2

average mass of one molecule of that compound compared with 1/12 mass of the carbon 12 isotope

Question 3

what does RMM stand for

Answer 3

relative molecular mass

Question 4

how to calculate RMM

Answer 4

1. count the number of atoms of each element
2. multiply the mass number of that element by how many atoms of that element there is. repeat for all elements and add them together= RMM

Question 5

how to calculate % by mass

Answer 5

step 1. calculate RMM

step 2. put mass no. of element you are trying to find over the RMM (if there is more than 1 atom of that element multiply the mass no by the number of atoms before putting it over the RMM)

step 3. multiply mass number over RMM by 100 = % by mass

Question 6

how to calculate empirical formula

Answer 6

step 1. in the question it will say there is xg of Y. find the atomic mass number of the elements and divide mass by atomic mass. repeat for each element.

step 2. take the smallest answer and divide it into all the answers you found in step 1

step 3. write formula using answers.

Question 7

how to calculate molecular formula

Answer 7

step1. find empirical formula is not given in the question

step 2. divide RMM given in the question by the RMM of the empirical formula

step 3. multiply empirivcal formula by number obtained in step 2

Question 8

how to calculate Moles

Answer 8

step 1. find RMM of compound given

step 2. moles = mass divided by RMM (remember the triangle

Question 9

how to calculate number of molecules

Answer 9

step 1. number of molecules is = to moles X Avogadros constant.

NOTE: often you have to work your way down to moles ie convert grams to moles before you can calculate the molecules

Question 10

how to calculate number of atoms

Answer 10

step 1. calculate number of molecules

step 2. find number of atoms in compound ie CH4 has 5 atoms

step 3. multiply number of molecules by no of atoms

Question 11

how to calculate relating mole of an element in a molecule

Answer 11

step 1. calculate total moles of the compound

step 2. the number beside the element you are trying to find is the number of moles is has. multiply that number by the total found in step one

Question 12

How to balance an equation

Answer 12

Make table showing how many of each element are on both the left and right side
Figure out what number goes infront of each compound to balance the atoms
Go in order of the atoms on the left side of equation
Remember when changing the number of 1 element you are probably changing the no of another

Question 13

How to find limiting reagent

Answer 13

Find moles of each reactant
Figure out ratio needed for reaction to take place to find the min amount of a reactant needed for a reaction to take place
If this no is bigger than the no of moles you found in step 1 it is in excess and rhe other is limiting

Question 14

What sentence do you use to explain limiting reagents

Answer 14

If we start with x no of y we need x no of moles of z for the reaction to take place. We used more z than needed so z is in excess and y is limiting

Question 15

How to find no of moles of product from limiting reagent

Answer 15

Use ratio of limiting reagent to the product

Question 16

How to find percentage yield

Answer 16

Actual yield / theoretical yield x100
Actual yield is what you formed vs theoretical= what you should have formed

Question 17

Why is the actual yield always less than expected

Answer 17

Reaction may be incomplete so not all reactants may be used up
Product is lost when transferring from 1 container to another
Unwanted side reactions taking place