stochiometry (1.4-1.5)

Question 1

whats the standard unit of amount of susbtance

Answer 1

the mole

Question 2

what does the mole contain

Answer 2

exactly the number of elementary given by the avogrados constant (6.0 X 10ˆ23)

Question 3

what are the mass of an atom compared to

Answer 3

carbon 12 and are expressed as relative atomic mass Ar and relative formula mass Mr

Question 4

whats the empircal formula

Answer 4

simplest whole ratio of atoms of each element present in compound

Question 5

whats molecular formula

Answer 5

ratio shows actual amount of atoms of each element present in that compound

Question 6

how do you prepare a standard solution

Answer 6

-weigh weighing boat, note mass
-add about 2g acid, note mass
-add acid to washed beaker
-reqeigh the boat and wirte the weight
-add 50ml distileled water to beaker stir to dissolve crystals crush them-put a washed funne into washed volumetric flask and carefully pour the acid down stirring rod into funnel do not lose any acid
-return rod to beaker and add 50 ml to rinse beaker and add to flask rinse rod and funnel, do not go over 250ml
-put lid into flask secure base and shake

Question 7

convert from cm cubed to dm cubed

Answer 7

cm-dm = /1000

Question 8

how can you express conecntration

Answer 8

[ ] square brackets

Question 9

describe how to carry out an acid based titration

Answer 9

-rinse buretter with small amount of acid, throw to waste
-fill burette with acid until bottom of miniscus 0.00 line
-rinse pipette with base/ alklai
-use pump and volumetric pipetter to pipette 25 ml of base into conical flask
-add a few drops of indicator eg.phenolpthalein indicator
-add acid washing and swirling until you achieve a pale pink color
-record volume on burette
-wash out flask and repeat
-achieve until you have 2 concordant results (within 0.2)

Question 10

how do you calculate uncertaintys

Answer 10

divide the uncertainty of aparatus by weight or value of measured eg mass times by 100% and all uncertaintys, and calculate the percentage difference from og value

Question 11

what does avogrados law state

Answer 11

equal volumes of all gases under same conditions (temp and pressure) contain euqal numbers of mlecules (22.7 dm cubed molˆ-1)

Question 12

equation relating gases and moles

Answer 12

volume= mol * 22.7

Question 13

whats the mr of a molecule

Answer 13

the sum of all the relative atomic masses

Question 14

whats the Ar

Answer 14

atomic masses of the constituent elements in the molecule

Question 15

what are the standar conditions

Answer 15

273K, 100KPa

Question 16

what is an ideal gas

Answer 16

-moving particles with negible volume and intermoecular forces
-all collisions between particles are considered elastic and frictionless( no energy loss in motion or collision)
-moelcules constantly moving in random directions with distribution of speeds
-molecules of gas are indistinguishible small hard spheres that are point-like

Question 17

why are gases no ideal

Answer 17

-some factors such as gravity will cause particles to have variable concentrations
-particles have intermolecular forces attractive and electrons are repulsive

Question 18

what causes the attractive forces between the particles to be negiligible

Answer 18

great seperation of the particles

Question 19

what happens to pressure when volume is halved

Answer 19

doubles the collisions, doubles pressure

Question 20

what happens when double numb of moles to pressure

Answer 20

double the numb of collisions, doubles pressure

Question 21

what happens when double temp to pressure

Answer 21

double temp you double the KE and therefore double the collisions and the pressure

Question 22

describe graph of p against v

Answer 22

they are inversely porportional
when its p vs 1/v then its a positive correlation, directly porportional

Question 23

describe graph of v against T

Answer 23

directly porportional

Question 24

describe graph of T against P

Answer 24

directly porportional

Question 25

what are characterisitcs good to be used as standard solutions

Answer 25

it has high relative molecular mass- reduces our uncertainty it is soluble- all dissolve it is stable in the atmosphere (non-hygroscopic and unreactive)- non-hygroscopis= does not absorb water from atmosphere unreactive

Question 26

accuracy

Answer 26

all results are equal or close to true value, results which are inaccurate are because of random erros eg incorrect use of equipment, human errors

Question 27

precise

Answer 27

very close to average, can be inaccurate because of systematic errors eg. un calibrated balance