Flashcards in unit 3 test Deck (35)

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1

## what is a limiting reagent/ reactant?

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

2

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

### the problem gives you the mass for each reactant.

3

## how to find the moles using mass?

### n = m/M

4

## how do you know when a reaction is finished?

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

5

## what is stoichiometry?

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

6

## what is a mole ratio?

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

7

## how do you use a mole ratio?

### 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 :)

8

## what is the strategy for stoichiometry?

###
**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

9

## what is a hydrate?

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

10

## how do you find %H2O

### mass of H2O/mass of hydrated compound

11

## what is a hydrate with water removed called?

###
an anhydrous compound

12

## what is an emperical formula?

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

13

## what is a molecular formula?

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

14

## what is the law of definite proportions?

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

15

## what is the percentage composition?

### the relative mass of each element in the compound.

16

## what is the emperical formula rhyme?

###
percent to mass

mass to mole

divide by small

multiply til whole.`

17

## how to find the emperical formula using % composition

###
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.

18

## how to find the chemical formula of a hydrate?

### 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

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)

###
< X Na X M>

N (things)------------ n (mols) --------- m (mass)

/ Na >

20

## how to do significant digits?

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

21

## wait i see how to do sig. dig.

###
-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.

22

## what is the value of avogadros contant?

### 6.022X10^23.

23

## what is percent yield?

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

24

## how do you measure the % yield?

### actual yield over theoretical yield X 100

25

## what is theoretical yield?

### the calculated quantity based on stoichometry.

26

## what is actual yield?

### gathered experimentally.

27

## how to find % yield?

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

28

## what is molar mass?

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

29

## how to find molecular formula

### 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?

30