chemistry question paper 1

Question 1

in a titration without changing equpiment how would you reudce % uncertainty using burette

Answer 1

use a larger mass of solid
and this producers a larger titre

Question 2

how t prepare a solution of 250cm3 containing MHCO3

Answer 2

: transfers known mass of solid
a) Weigh the sample bottle containing the solid on a (2 dp)
balance
b) Transfer to beaker* and reweigh sample bottle
c) Record the difference in mass

a) Add distilled / deionised water
b) Stir (with a glass rod) or swirl
c) Until all solid has dissolved
Stage 3: Transfer, washing and agitation
a) Transfer to volumetric / graduated flask. Allow if a clear
description/diagram given eg long necked flask with
250cm3 mark
b) With washings
c) Make up to 250cm3 / mark with water
d) Shakes/inverts/mixes

Question 3

in terms of strucutre anad bondindg explain why mag hasa higher bp and bromine

Answer 3

M1 Bromine is (simple) molecular / simple molecules
M2 Magnesium is metallic / consists of (positive) ions in a
(sea) of delocalised electrons
Strength
M3 Br2 has weak (van der Waals) forces between the
molecules / weak IMFs
M4 so more energy is needed to overcome the Stronger
(metallic) bonds or converse. The comparison could be direct
or implied.
Liquid range
M5 Mg has a much greater liquid range because forces of
attraction in liquid / molten metal are strong(er) OR converse
argument for Br2

Question 4

explain how ions are accelerated deteted and how their tof is determined

Answer 4

ions attracted towards neg charged plate
ios detetced by electron gained
abundace is proportional to current generated

Question 5

a soultion of sdoium chlorate was added to a colourless sol of pot iodide
suggest whats observed

Answer 5

Goes brown (or shades of brown)
Due to iodine or I3
−
Because I− oxidised

Question 6

explain why air bubble increases the fonal burette reading in rough titration

Answer 6

some sol replaces air bubblr

Question 7

nacl and na2co3 reagent and observation

Answer 7

no observation
effervesence

Question 8

one pbservation of magneium and steam

Answer 8

white solid bright white light

Question 9

forces in chlorine

Answer 9

(Random) movement of electrons in one molecule (creates a dipole) /
a (temporary) dipole is formed in one molecule / an imbalance in
electron density in one molecule
Induces a dipole in a neighbouring molecule.
(These) temporary dipoles attract / temporary attraction between δ+
and δ–

Question 10

chlrone and naoh

Answer 10

Cl2 + 2 NaOH → NaCl + NaClO + H2O

Question 11

how to show a sample contains hcl

Answer 11

Effervescence (with Na2CO3,) so contains H+ ions / Effervescence
(with Na2CO3,) so is acidic
White ppt (with AgNO3,) so contains chloride ions

Question 12

describe a series of tests that the student can use to show that sol c contains ammonia sulfate

Answer 12

(Warm with some) NaOH,
Damp red litmus at the mouth of the tube turns blue
Add (acidified) BaCl 2 / Ba(NO3)2
White ppt formed

Question 13

state the trend in the atomic radius of the elements down group 2 from mg to ba

Answer 13

increaeses
more energy levesl for electrons

Question 14

use of baso4

Answer 14

x rays

Question 15

improvements for a standard solution method

Answer 15

recoed all masses to 2dp
weigh by difference
wash beaker into flask after the solution is trasnferred to volumetric flask

Question 16

concenrtarted sulfuric acid reacts with solid soidum chlride and with soidum bromide state one similarit and one diff in the reacrions

Answer 16

form hydorgn sulfide
bromide undergoes a redox reaction

Question 17

inc temp in exo reaction effect on kc

Answer 17

inc
shifts to exo direction to oppose change dec in temp

Question 18

what improves accuracy pf titres

Answer 18

rinsing conical flask with water between each titration

Question 19

what decreases uncertainty in mean titre

Answer 19

use a more dilute sosl of soidum hyrodxide in the buretter