Chemistry MCQ thread...

[ambitious1]

Oh, ok. Thanks Hassam. =)

 

[xHazeMx]

does ethanoic acid dissolve completely in water? and does it form hydrogen bonds with water molcules ?

 

[Xthegreat]

ethanoic acid dissolves partially in water, that's why it's a weak acid

it does not have a H that is covalently bonded F/ O /N , so no.

 

[xHazeMx]

but it MIXES completely with water right?

 

[xHazeMx]

A compound X has all of the properties below.
• It is a liquid at 25°C.
• It mixes completely with water.
• It reacts with aqueous sodium hydroxide.

What could X be?
A ethanoic acid
B ethanol
C ethene
D ethyl ethanoate

 

[hassam]

@xTHE GREAT....ehtnaoic acid cn form hydrogen bonds with water cos it contains COOH...which has the -OH groups...in which H is bonded to OXYGEN ATOM

 

[hassam]

that A...xHaZEmX

 

[xHazeMx]

answer with explanation

 

[xHazeMx]

that A...xHaZEmX

why it can't be ethanol?

 

[xHazeMx]

why is it C and not B or A ?

 

[Zishi]

answer with explanation

Make a balanced equation of reaction of NaCl with water to give cl2 , h2 and NaOH as products.

that A...xHaZEmX

why it can't be ethanol?

Because ethanol doesn't reacts with NaOH.

why is it C and not B or A ?

It's B.

 

[xHazeMx]

it's B sorry, but why the other choices are wrong?

 

[xHazeMx]

@zishi,
2NaCl + 2H2O ------> H2 + Cl2 + 2NaOH
i got the answer , thanks

 

[hassam]

A mixture containing 0.100 mol of CaCO3 and 0.100 mol of CaO are introduced
into an evacuated 0.01 m3 vessel. The vessel is heated to a constant
temperature of 385 K such that the equilibrium below is established.
CaCO3(s) CaO(s) + CO2(g)
The partial pressure of carbon dioxide at equilibrium is then found to be 0.220
atm.
What is the total mass of CaCO3 at equilibrium after an additional 0.300 atm of
carbon dioxide is pumped into the vessel?
A 0.530 g
B 10.0 g
C 12.5 g
D 19.5 g

 

[xHazeMx]

A mixture containing 0.100 mol of CaCO3 and 0.100 mol of CaO are introduced
into an evacuated 0.01 m3 vessel. The vessel is heated to a constant
temperature of 385 K such that the equilibrium below is established.
CaCO3(s) CaO(s) + CO2(g)
The partial pressure of carbon dioxide at equilibrium is then found to be 0.220
atm.
What is the total mass of CaCO3 at equilibrium after an additional 0.300 atm of
carbon dioxide is pumped into the vessel?
A 0.530 g
B 10.0 g
C 12.5 g
D 19.5 g

someone show the calculation for this question. i dont get it

 

[xHazeMx]

answer with explanation

Make a balanced equation of reaction of NaCl with water to give cl2 , h2 and NaOH as products.

that A...xHaZEmX

why it can't be ethanol?

Because ethanol doesn't reacts with NaOH.

why is it C and not B or A ?

It's B.

ethanol reacts with NaOH forming CH3CH2ONa and water right? so why still ethanol remain as a wrong answer ?

 

[Zishi]

A mixture containing 0.100 mol of CaCO3 and 0.100 mol of CaO are introduced
into an evacuated 0.01 m3 vessel. The vessel is heated to a constant
temperature of 385 K such that the equilibrium below is established.
CaCO3(s) CaO(s) + CO2(g)
The partial pressure of carbon dioxide at equilibrium is then found to be 0.220
atm.
What is the total mass of CaCO3 at equilibrium after an additional 0.300 atm of
carbon dioxide is pumped into the vessel?
A 0.530 g
B 10.0 g
C 12.5 g
D 19.5 g

Wait for my answer.

Make a balanced equation of reaction of NaCl with water to give cl2 , h2 and NaOH as products.

ethanol reacts with NaOH forming CH3CH2ONa and water right? so why still ethanol remain as a wrong answer ?

No, only sodium metal reacts with alcohols, and nothing else like NaOH.

 

[bionology]

how to solve this one? Anyone please.... :unknown:

Use of the Data Booklet is relevant to this question.
The enthalpy change of formation, ΔHf, of hydrated calcium ions is the enthalpy change of the following reaction.

Ca(s) + aq – 2e– → Ca2+(aq)

The following enthalpy changes are not quoted in the Data Booklet.

Ca(s) → Ca(g) ΔHa = 177 kJ mol–1
Ca2+(g) + aq → Ca2+(aq) ΔHhyd = –1565 kJ mol–1

What is the enthalpy change of formation of hydrated calcium ions?
A –1388 kJ mol–1
B –798 kJ mol–1
C –238 kJ mol–1
D +352 kJ mol–1

 

[Zishi]

A mixture containing 0.100 mol of CaCO3 and 0.100 mol of CaO are introduced
into an evacuated 0.01 m3 vessel. The vessel is heated to a constant
temperature of 385 K such that the equilibrium below is established.
CaCO3(s) CaO(s) + CO2(g)
The partial pressure of carbon dioxide at equilibrium is then found to be 0.220
atm.
What is the total mass of CaCO3 at equilibrium after an additional 0.300 atm of
carbon dioxide is pumped into the vessel?
A 0.530 g
B 10.0 g
C 12.5 g
D 19.5 g

My answer is C.

 

[Zishi]

how to solve this one? Anyone please.... :unknown:

Use of the Data Booklet is relevant to this question.
The enthalpy change of formation, ΔHf, of hydrated calcium ions is the enthalpy change of the following reaction.

Ca(s) + aq – 2e– → Ca2+(aq)

The following enthalpy changes are not quoted in the Data Booklet.

Ca(s) → Ca(g) ΔHa = 177 kJ mol–1
Ca2+(g) + aq → Ca2+(aq) ΔHhyd = –1565 kJ mol–1

What is the enthalpy change of formation of hydrated calcium ions?
A –1388 kJ mol–1
B –798 kJ mol–1
C –238 kJ mol–1
D +352 kJ mol–1

It's D. First IE of calcium = 590
Second IE of calcium = 1150

To convert solid Ca into gas you need 177 kJmol-1 energy, and then to convert it to 2+ ions you need 590+1150 energy. Then for hydrating the ions the energy change is 1565kjmol-1. So total energy change = 177+590+1150-1565 = +352 kJmol-1