# Chemistry questions

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#1
Can i have some help with these questions?

The concentration of ClO– ions in bleach solution can be found by reaction with
iodide ions.
The overall equation for this reaction is shown.
ClO- + 2I- + 2H+ → I2 + Cl- + H2O
A sample of bleach solution was found to contain ClO– ions with a concentration of
0.0109 mol dm–3
Potassium iodide is added to a 20.0 cm3 portion of this bleach solution.
Calculate the mass, in mg, of potassium iodide needed to react with all of the
ClO– ions in the sample of bleach.
Give one observation during this reaction.

2)A sample of bromine was analysed in a time of flight (TOF) mass spectrometer and
found to contain two isotopes, 79Br and 81Br
After electron impact ionisation, all of the ions were accelerated to the same
kinetic energy (KE) and then travelled through a flight tube that was 0.950 m long.
0 8 . 1 The 79Br+ ions took 6.69 x 10–4 s to travel through the flight tube.
Calculate the mass, in kg, of one ion of 79Br+
Calculate the time taken for the 81Br+ ions to travel through the same flight tube.
Last edited by username3725268; 2 years ago
0
2 years ago
#2
n(ClO-) = 2.18 x 10^-4 mol
n(I-) = 4.36 x 10^-4 mol
so mass of KI = 72.4 mg
Brown solution formed

mass of Br-79 ion = 1.31 x 10^-25 kg
speed of the ion = 1420 ms^-1
KE same for both, so 1/2mv^2 same
1/2 x 79 x 1420^2 = 1/2 x 81 x v^2
v = 1402 ms^-1
time = 0.950 / 1402 = 6.77x 10^-4 s
0
2 years ago
#3
(Original post by bhayat)
could someone plz help me with this question
6. Separate unlabelled solid samples of three anhydrous sodium compounds are
provided for a student to identify.
These compounds are known to be sodium carbonate, sodium fluoride and
sodium chloride but it is not known which sample is which.
Outline a logical sequence of test-tube reactions that the student could carry out to
identify each of these compounds.
Include the observations the student would expect to make.
Give equations, including state symbols, for any reactions that would take place.
[6 marks]
Add dilute HCl. Effervescence with sodium carbonate
Add AgNO3. White ppt with NaCl but no ppt with NaF.
0
2 years ago
#4
(Original post by bhayat)

Silicon tetrafluoride (SiF4) is a tetrahedral molecule.
Deduce the type of intermolecular forces in SiF4
Explain how this type of intermolecular force arises and why no other type of
intermolecular force exists in a sample of SiF4
[3 marks]
Induced dipole-dipole because it is non-polar
0
2 years ago
#5
(Original post by bhayat)
how did you get the mass of br-79
1 mol of Br-79 weighs 79 g or 0.079 kg
so 1 molecule of Br-79 weighs 0.079kg/6.02x10^23
0
2 years ago
#6
(Original post by bhayat)
swear this question is impossible!!!
This question is about enthalpy changes.
0 3 . 1 When ethanoic acid reacts with sodium hydroxide, the enthalpy change, ∆H, is
–56.1 kJ mol–1
CH3COOH(aq) + NaOH(aq) ⟶ CH3COONa(aq) + H2O(l)
Calculate the temperature rise when 25 cm3 of 2.0 mol dm–3 aqueous ethanoic acid
react with 25 cm3 of 2.0 mol dm–3 aqueous sodium hydroxide.
Assume that both solutions have the same initial temperature, have a density of
1.0 g cm–3 and a specific heat capacity of 4.18 J K–1 g–1
You need to show your attempt.
0
2 years ago
#7
(Original post by bhayat)
this is not homework, i am currently revising for my year 1 as exams and i am doing past paper questions
0
2 years ago
#8
(Original post by bhayat)
Which compound has the highest boiling point?
[1 mark]
A butanal
B butan-2-ol
C but-2-ene
D 1-fluorobutane

is this one A
No
0
2 years ago
#9
(Original post by bhayat)
C because of the double bond???
No, boiling point is not due to the bonds between the atoms in a molecule (intramolecular forces). It is due to the intermolecular forces (force between the molecules).
A has permanent dipole-dipole forces
B has hydrogen bonds
C has induced dipole-dipole forces
D has permanent dipole-dipole forces
Which is strongest?
0
2 years ago
#10
(Original post by bhayat)
B because Hydrogen bonds r the strongest bonds????
yes
(Original post by bhayat)
Which element has the highest first ionisation energy?
[1 mark]
A Aluminium
B Phosphorus
C Silicon
D Sulfur

is this one B
Yes
0
2 years ago
#11
(Original post by bhayat)
Which species could act as a nucleophile?
[1 mark]
A BH3
B NH4+
C PH3
D SiH4

is this C
yes
0
2 years ago
#12
yes.
1,4 isomer
2,4 isomer
1,2 isomer
1,1 isomer
2,2 isomer
2,3 isomer
0
2 years ago
#13
(Original post by bhayat)
Which molecule does not have a permanent dipole?
[1 mark]
A CH3Br
B CH2Br2
C CHBr3
D CBr4

is this D
due to it being symmetrical
Yes
0
2 years ago
#14
(Original post by bhayat)
swear this question is impossible!!!
This question is about enthalpy changes.
0 3 . 1 When ethanoic acid reacts with sodium hydroxide, the enthalpy change, ∆H, is
–56.1 kJ mol–1
CH3COOH(aq) + NaOH(aq) ⟶ CH3COONa(aq) + H2O(l)
Calculate the temperature rise when 25 cm3 of 2.0 mol dm–3 aqueous ethanoic acid
react with 25 cm3 of 2.0 mol dm–3 aqueous sodium hydroxide.
Assume that both solutions have the same initial temperature, have a density of
1.0 g cm–3 and a specific heat capacity of 4.18 J K–1 g–1
Number of moles of acid and alkali are 0.05 mol
so 2805 J of heat is released
hence the temperature rise is 13.4K
(use a mass of 50 g because the heat is dispersed in 50 cm3 of solution)
0
2 years ago
#15
(Original post by bhayat)
I totally do not understand how to find out the number of molecules?Can u help

A gas cylinder contains 5.0 kg of propane.

How many propane molecules are in the cylinder?
The Avogadro constant, L = 6.022 × 1023 mol–1
[1 mark]
A 6.8 × 1022
B 7.2 × 1022
C 6.8 × 1025
D 7.2 × 1025
Find number of moles of propane (113.6 mol)
1 mol contains 6.02 x 10^23 molecules
so 5.0 kg of propane, which is 113.6 mol of propane contains 6.8 x 10^25 molecules so C
0
2 years ago
#16
(Original post by bhayat)
Draw the shape of a molecule of krypton difluoride (KrF2).
Include in your answer any lone pairs of electrons that influence the shape.
Name the shape produced by the atoms in a KrF2 molecule and suggest a
bond angle.

Got another question
I worked out KrF2 will have 2 bonding pairs 3 loan pairs
would the shape not be trigonal bypriomidal

but my mate said to me it is linear and bond angle 180

so i am unsure what the answer is
It is linear and bond angle 180 degrees

Think of the shape when there are 5 bond pairs. It is trigonal bipyramidal. Now replace 3 bond pairs with lone pairs. Bearing in mind lp-lp repulsions > lp-bp repulsions > bp-bp repulsions, convince yourself that the shape which minimises the electronic repulsion is a linear shape. The lone pair will occupy equatorial positions https://d2jmvrsizmvf4x.cloudfront.ne...T_Image668.gif
1
2 years ago
#17
(Original post by bhayat)
cant seem to know how to get the speed for the ion as 1420
i keep getting 0.950/6.69*10-4=1.42*10-5
https://www.wolframalpha.com/input/?...(6.69*10%5E-4)
0
2 years ago
#18
(Original post by bhayat)
Which statement is correct about the fractional distillation of crude oil?
[1 mark]
A A zeolite catalyst is used.
B Each fraction contains a mixture of hydrocarbons.
C Gaseous fractions are formed by breaking covalent bonds.
D The fractionating column is hottest at the top.

is this one B
Yes.
Each fraction contains hydrocarbons in a certain range of carbon atoms
Hottest at the bottom since less volatile components collect at the bottom (e.g bitumen)
0
2 years ago
#19
(Original post by bhayat)
Which statement is correct about the fractional distillation of crude oil?
[1 mark]
A A zeolite catalyst is used.
B Each fraction contains a mixture of hydrocarbons.
C Gaseous fractions are formed by breaking covalent bonds.
D The fractionating column is hottest at the top.

is this one B
I would say it’s B
0
2 years ago
#20
(Original post by bhayat)
Which statement is correct about poly(chloroethene)?
[1 mark]
A It has the empirical formula CHCl
B It decolourises bromine water.
C Its brittleness is reduced by plasticisers.
D Its polymer chain contains alternate single and double bonds.

is this D
No. The polymer chain contains only single bonds. If it contained double bonds B would be correct too. Only 1 option can be correct.
1
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