kumpulan berlian

7/27/2019 Kumpulan Berlian

1/7

(c) An experiment is carried out to construct an ionic equation for an insoluble salt,lead (II) chromate (VI).

A fixed volume of 5.00 cm3 of 1.0 mol dm-3 lead (II) nitrate, Pb(NO3)2solution is placed into each of the 8 test tubes of the same size.

Different volume of 1.0 mol dm-3 potassium chromate (VI), K2CrO4 solution

is added to each test tube. The height of the yellow precipitate, lead (II) chromate (VI) formed into

each test tube is measured, recorded and plotted in Graph 8.Satu eksperimen dijalankan untuk membina persamaan ion untuk garam takterlarukan, plumbum (II) kromat(VI).

Isipadu tetap 5.00 cm3 1.0 mol dm-3 larutan plumbum(II) nitrat Pb(NO3)2diisikan ke dalam setiap 8 tabung uji yang sama saiz.

Isipadu yang berbeza larutan kalium kromat (VI), K2CrO4 1.0 mol dm-3

ditambahkan ke dalam setiap tabung uji.

Tinggi mendakan kuning plumbum (II) kromat (VI) yang terbentuk dalamsetiap tabung uji diukur, direkod dan diplot dalam Graf 8.

0 1 2 3 4 5 6 7 8

1

2

3

4

5

6

7

Height of lead (II) chromate(VI) precipitate / cm

Tinggi mendakan plumbum(II) kromat (VI) / cm

Volume of potassium chromate(VI) solution, K2CrO4 / cm

3

Isipadu larutan kalium

kromat(VI), K2CrO4 / cm3


2/7

Based on Graph 8

Berdasarkan Graf 8

(i) Calculate

Hitungkan

The number of moles of lead (II) ions used.

Bilangan mol ion plumbum (II) yang digunakan.

The number of moles of potassium chromate (VI) that has reactedcompletely with 5.00 cm3 of lead (II) nitrate.

Bilangan mol kalium kromat (VI) yang bertindak balas selengkapnyadengan 5.00 cm3 plumbum (II) nitrat.

[4 marks][4 markah]

(ii) Based on the answer in (c) (i), construct an ionic equation for the formation

of lead (II) chromate (VI).

Berdasarkan jawapan anda di (c) (i), bina persamaan ion untuk

pembentukan plumbum (II) kromat (VI).

[2 marks][2 markah]

(iii) Explain why

Terangkan mengapa

The height of precipitate formed increases and then remain constantTinggi mendakan bertambah dan kemudian menjadi malar.

The colour change in the solution above the precipitate.Perubahan warna larutan di bahagian atas mendakan.

The eight test tubes used are of the same size.Kelapan-lapan tabung uji yang digunakan adalah bersaizsama.

[6 marks][6 markah]


3/7

(i) Number of moles of lead(II) ions, Pb2+

= number of moles of lead(II) nitrate, Pb(NO3)2

= 1.0 x

= 0.005 mol

Number of moles of chromate(VI) ions, CrO42-

= number of moles of potassium chromate(VI),K2CrO4

= 1.0 x

= 0.005 mol

(ii)1 mol of chromate(VI) ions, CrO42- reacted

completely with 1 mol of lead(II) ions, Pb2+

.

The ionic equation for the reaction is:

Pb2+

+ CrO42-

PbCrO4

5

1000

5

1000


4/7

(iii)- The height of precipitate formed increases for thefirst 4 test tubes because as the volume of potassiumchromate(VI) increases, more PRECIPITATE /lead(II)

chromate(VI) is formed- The height of precipitate formed becomes constantwhen all Pb

2+have reacted completely.

- colourless to yellow- Presence of chromate(VI) ions give the yellow colourto the solution // Chromate(VI) ions in the first 5 testtubes are all reacted // In the last 3 test tubes,

chromate(VI) ions are in excess

-To ensure the height of precipitate represents theamount of precipitate formed- because diameter of the test tubes are the same


5/7

2 Diagram 4.1 shows the apparatus set-upfor the neutralisation reaction between nitric

acid and potassium hydroxide solution for preparation of salt X.Rajah 4.1 menunjukkan susunan radas untuk tindak balas peneutralan antaraasid nitrik dan larutan kalium hidroksida untuk penyediaan garam X.

Diagram 4.1Rajah 4.1

(a) State the colour change of the solution in the conical flask at the end point.Nyatakan perubahan warna larutan dalam kelalang kon pada takatakhir.

.

.[1 mark]

(b) Calculate the maximum mass of the salt X formed.[Molar mass of salt X = 101 g mol -1]

Hitungkan jisim maksimum garam X yang terbentuk.[Jisim molar garam X = 101 g mol-1]

20.0 cm3 of 0.5 mol dm-3

potassium hydroxidesolution + phenolphthaleinindicator

20.0 cm3 larutan kaliumhidroksida 0.5 mol dm

-3+penunjuk fenolftalein

20.0 cm3 of 0.5 mol dm-3 nitricacid

20.0 cm3asid nitrik 0.5mol


6/7

[3 marks]

(c) (i) The experiment is repeated with 0.5 mol dm -3 sulphuric acid to replacenitric acid. Predict the volume of sulphuric acid needed to neutralize

completely.Eksperimen itu diulangi dengan menggunakan 0.5 mol dm-3 asidsulfurik bagi menggantikan asid nitrik. Ramalkan isipadu asid sulfurikyang diperlukan untuk peneutralan lengkap.

.[1 mark]

(ii) Explain your answer in (c) (i).Terangkan jawapan anda dalam (c) (i).

.

.

.[2 marks]

(iii) Write the ionic equation for the reaction in (c) (i).Tuliskan persamaan ion bagi tindak balas dalam (c) (i).

.

[1 mark]

(d) Explain this statement.

(i) In acid-base titration, only 2 or 3 drops of anindicator should be used.

(ii) Burette and pipettes must be rinsed with thesolution to be measured .


7/7

(i) This is because most of the indicators are weakacid or base that will affect the pH of the solution ifused in excess.

(ii) To make sure the solution used is not diluted bydroplets of water on the walls of burette or pipette.

kumpulan berlian

Documents