unit 3 test

Question 1

what is a limiting reagent/ reactant?

Answer 1

reactant that limits the amount of a substance that can be created

Question 2

how do you know when you have a limiting reagent question?

Answer 2

the problem gives you the mass for each reactant.

Question 3

how to find the moles using mass?

Answer 3

n = m/M

Question 4

how do you know when a reaction is finished?

Answer 4

the reaction is ended, there is no more of one reactant or no more changes are happening.

Question 5

what is stoichiometry?

Answer 5

used to predict the amount of a product in a reaction.

Question 6

what is a mole ratio?

Answer 6

helps us find how many moles of an unknown substance there are. set up with a known ratio and an unknown ratio.

Question 7

how do you use a mole ratio?

Answer 7

set up an unknown ration with X unknown on the top, on the other side of the ratio use the same reactants using the molecules in the balanced chemical equations. multiply the number you found for # of mols of a reactant by the top of your known ratio and divide by the bottom of the ratio. hope that makes sense :)

Question 8

what is the strategy for stoichiometry?

Answer 8

number of moles are the key
* start with a balanced chemical equation.
mass A/ Molar mass A -> mol A – mol ratio–> mol B X molar mass B–> mass B

Question 9

what is a hydrate?

Answer 9

in an ionic compound that has a crystal like structure (all ionic compounds), each unit has an associated amount of water molecules in it.

Question 10

how do you find %H2O

Answer 10

mass of H2O/mass of hydrated compound

Question 11

what is a hydrate with water removed called?

Answer 11

an anhydrous compound

Question 12

what is an emperical formula?

Answer 12

the simplest formula such as CH, there are many molecular formulas containing CH, but CH is the simplest form of it.

Question 13

what is a molecular formula?

Answer 13

the actual formula, makes up a formula unit depending in the atoms of each element.

Question 14

what is the law of definite proportions?

Answer 14

also known as the law of constant composition, states that all samples of a compound have the same proportions by mass.

Question 15

what is the percentage composition?

Answer 15

the relative mass of each element in the compound.

Question 16

what is the emperical formula rhyme?

Answer 16

percent to mass
mass to mole
divide by small
multiply til whole.`

Question 17

how to find the emperical formula using % composition

Answer 17

Assume you have 100g of a substance, determine the number or mol in each element from their new mass given,
determine the lowest number of mols in the denominator.

Question 18

how to find the chemical formula of a hydrate?

Answer 18

write out givens and required, find the molar mass of water, find mols of water, find the mols of other compound, find the ratio of H2O:element

Question 19

how do you go from number of atoms to mols to mass? (diagram thing but crudely formatted bc i dont want to pay for premium)

Answer 19

< X Na X M>
N (things)———— n (mols) ——— m (mass)
/ Na >

Question 20

how to do significant digits?

Answer 20

good lord if i know just make a guess maybe like 4 who knows. if you know hoy to plz let me know thanks.

Question 21

wait i see how to do sig. dig.

Answer 21

-non zero digits in your starting measurement are valid.
-zeros between non zeroes such as 101 are significant
-zeroes to the left of non zeroes are only placeholders, and therefore are not significant.
numbers that are counted, such as an apple, are exact therefore infinite sig. digits.

Question 22

what is the value of avogadros contant?

Answer 22

6.022X10^23.

Question 23

what is percent yield?

Answer 23

a way of comparing the experimental value to the theoretical yield, measures the efficiency of a reaction.

Question 24

how do you measure the % yield?

Answer 24

actual yield over theoretical yield X 100

Question 25

what is theoretical yield?

Answer 25

the calculated quantity based on stoichometry.

Question 26

what is actual yield?

Answer 26

gathered experimentally.

Question 27

how to find % yield?

Answer 27

need a mass of a reactant and product. find mols of each.find mass from mols, find yield with given weight and found weight.

Question 28

what is molar mass?

Answer 28

the mass of one mol of a substance. can be found using periodic table. units of g/mol.

Question 29

how to find molecular formula

Answer 29

find emperical formula by assuming 100g of the compoiuund.divide by molar mass to find mols. divide by the smallest. find the mass of compound, divide by given mass of the 1 mol of compound. makes sense?

Question 30

what causes % yield to be less than 100%

Answer 30

incomplete reaction, inability to gather all of the product, impure reactant, competeing side reaction, incomplete transfer.

Question 31

what causes % yield to be more than 100%

Answer 31

a competing side reaction, or the product is wet. (water)

Question 32

when do you have to find a LR?

Answer 32

when you have a defined amount of two products

Question 33

how do you find moles using things or avocado?

Answer 33

n = N/NA

Question 34

what are two factors that influence the certainty of a measurement?

Answer 34

systematic error (measuring tool) and random error (made by the measurer)

Question 35

how do u find the ratio of water in hydrate?

Answer 35

divide mole of water by mole of compound.