Page 130 - Nilam_Publication_module_Chemistry_Form.pdf

MODULE • Chemistry Form 4

PREPARATION OF STANDARD SOLUTION / PENYEDIAAN LARUTAN PIAWAI

1 Standard solution is a solution in which its concentration is accurately known.
Larutan piawai ialah larutan yang kepekatannya diketahui dengan tepat.
2 The steps taken in preparing a standard solution are:
Langkah-langkah yang diambil dalam menyediakan larutan piawai adalah:
(a) Calculate the mass of solute needed to give the required volume and molarity.
Hitung jisim bahan larut yang diperlukan untuk menghasilkan isi padu dan kemolaran yang dikehendaki.
(b) The solute is weighed / Bahan larut ditimbang.
(c) The solute is completely dissolved in distilled water and then transferred to a volumetric flask partially filled with
distilled water.
Bahan larut dilarutkan sepenuhnya dalam air suling dan dipindahkan kepada kelalang volumetrik yang sebahagiannya sudah diisi
dengan air suling.
(d) Distilled water is added to the calibration mark of the volumetric flask and the flask is inverted to make sure
thorough mixing.
Air suling ditambah ke dalam kelalang volumetrik hingga tanda senggatan dan kelalang volumetrik ditelangkupkan beberapa kali
untuk memastikan campuran sekata.

PREPARATION OF A SOLUTION BY DILUTION / PENYEDIAAN LARUTAN SECARA PENCAIRAN

Adding water to the standard solution lowered the concentration of the solution. Since no solute is added, the amount of
solute in the solution before and after dilution remains unchanged:
Penambahan air kepada larutan piawai merendahkan kepekatan larutan tersebut. Oleh kerana tiada bahan terlarut yang ditambah, kandungan
bahan terlarut dalam larutan sebelum dan selepas pencairan tidak berubah:
Number of mol of solute before dilution = Number of mole of solute after dilution
Bilangan mol bahan terlarut sebelum pencairan Bilangan mol bahan terlarut selepas pencairan
M V M V
1
1 000 1 = 1 000 2
2
Therefore / Oleh itu,
M V = M V 2
1
1
2
M = Initial concentration of the solute / Kemolaran larutan awal
1
3
V = Initial volume of the solution in cm / Isipadu larutan awal dalam cm
3
1
M = Final concentration of the solute / Kemolaran larutan akhir
2
3
3
V = Final volume of the solution in cm / Isipadu larutan akhir dalam cm
2
Example / Contoh :
1 (a) What is meant by a standard solution / Apakah yang dimaksudkan dengan larutan piawai ?
Standard solution is a solution in which its concentration is accurately known.
(b) (i) You are given solid sodium hydroxide. Describe the procedure to prepare 500 cm of 1.0 mol dm sodium
–3
3
hydroxide solution. [Relative atomic mass: H = 1; O = 16; Na = 23]
Anda diberi pepejal natrium hidroksida. Huraikan kaedah untuk menyediakan 500 cm larutan natrium hidroksida
3
1.0 mol dm . [Jisim atom relatif: H = 1, O = 16, Na = 23]
–3
Calculate the mass of sodium hydroxide / Hitung jisim natrium hidroksida :
– Molar mass of NaOH / Jisim molar NaOH = 23 + 16 + 1 = 40 g mol –1
– Mol NaOH / Bilangan mol NaOH = 500 × 1.0/1 000 = 0.5 mol
– Mass of NaOH / Jisim NaOH = mol / Bilangan mol × molar mass / Jisim molar
–1
= 0.5 mol × 40 g mol = 20.0 g
Preparation of 500 cm 1.0 mol dm sodium hydroxide:
–3
3
–3
Penyediaan 500 cm larutan natrium hidroksida 1.0 mol dm :
3
– Weigh exactly 20.0 g of NaOH accurately using a weighing bottle .
Timbang 20.0 g NaOH dengan tepat menggunakan botol penimbang .
128
Nilam Publication Sdn. Bhd.

06-Chem F4 (3P).indd 128 12/9/2011 5:55:56 PM