Determine the molarity of a solution prepared by dissolving 5.0 g of NaOH in 450 mL of solution.

1. Determine the molarity of a solution prepared by dissolving 5.0 g of NaOH in 450 mL of solution. 1. 450 mL विलयन में 5.0 g NaOH घोलकर बनाए गए विलयन की मोलरता ज्ञात कीजिए। +

Given Data

Mass of NaOH = 5.0 g
Volume of solution = 450 mL
Molar mass of NaOH = 40 g mol⁻¹

Formula

M = n / V

Where:

M = Molarity
n = Number of moles of solute
V = Volume of solution in litres

Step 1: Calculate Moles of NaOH

Number of moles:

n = Mass / Molar Mass

n = 5.0 / 40

n = 0.125 mol

Step 2: Convert Volume into Litres

Given volume = 450 mL

Since:
1000 mL = 1 L

Therefore:

V = 450 / 1000

V = 0.450 L

Step 3: Calculate Molarity

Using:

M = n / V

M = 0.125 / 0.450

M = 0.2778 mol L⁻¹

Final Answer

The molarity of the NaOH solution is approximately 0.278 M.

Quick Method

M = (Mass × 1000) / (Molar Mass × Volume in mL)

Substituting:

M = (5.0 × 1000) / (40 × 450)

M = 0.278 M

Concept

Molarity is the number of moles of solute present in one litre of solution. Therefore, the volume must always be converted from mL to L before using the formula M = n/V.

दिया गया है

NaOH का द्रव्यमान = 5.0 g
विलयन का आयतन = 450 mL
NaOH का मोलर द्रव्यमान = 40 g mol⁻¹

सूत्र

M = n / V

जहाँ:

M = मोलरता
n = विलेय के मोलों की संख्या
V = विलयन का आयतन लीटर में

चरण 1: NaOH के मोल ज्ञात कीजिए

मोलों की संख्या:

n = द्रव्यमान / मोलर द्रव्यमान

n = 5.0 / 40

n = 0.125 mol

चरण 2: आयतन को लीटर में बदलें

दिया गया आयतन = 450 mL

हम जानते हैं:
1000 mL = 1 L

इसलिए:

V = 450 / 1000

V = 0.450 L

चरण 3: मोलरता ज्ञात कीजिए

सूत्र:

M = n / V

M = 0.125 / 0.450

M = 0.2778 mol L⁻¹

अंतिम उत्तर

NaOH विलयन की मोलरता लगभग 0.278 M है।

सीधी विधि

M = (द्रव्यमान × 1000) / (मोलर द्रव्यमान × आयतन mL में)

मान रखने पर:

M = (5.0 × 1000) / (40 × 450)

M = 0.278 M

Concept

मोलरता वह संख्या है जो बताती है कि एक लीटर विलयन में विलेय के कितने मोल उपस्थित हैं। इसलिए M = n/V सूत्र में आयतन को लीटर में लेना आवश्यक है।

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30 Related MCQs 30 संबंधित MCQs

1. The molar mass of NaOH is:

A. 23 g mol⁻¹

B. 40 g mol⁻¹

C. 58.5 g mol⁻¹

D. 18 g mol⁻¹

Answer: B. 40 g mol⁻¹

2. The number of moles present in 5.0 g NaOH is:

A. 0.025 mol

B. 0.125 mol

C. 0.25 mol

D. 1.25 mol

Answer: B. 0.125 mol

3. 450 mL is equal to:

A. 4.50 L

B. 0.045 L

C. 0.450 L

D. 45.0 L

Answer: C. 0.450 L

4. The formula for molarity is:

A. M = V/n

B. M = n/V

C. M = n × V

D. M = V × mass

Answer: B. M = n/V

5. The molarity of the given NaOH solution is approximately:

A. 0.028 M

B. 0.278 M

C. 2.78 M

D. 27.8 M

Answer: B. 0.278 M

6. Molarity is expressed in:

A. mol kg⁻¹

B. mol L⁻¹

C. g L⁻¹ only

D. kg mol⁻¹

Answer: B. mol L⁻¹

7. Before calculating molarity, 450 mL should be converted into:

A. kg

B. g

C. L

D. mol

Answer: C. L

8. One mole of NaOH has a mass of:

A. 20 g

B. 30 g

C. 40 g

D. 80 g

Answer: C. 40 g

9. The atomic mass of sodium is approximately:

A. 12

B. 23

C. 35.5

D. 40

Answer: B. 23

10. The molecular mass contribution of oxygen in NaOH is:

A. 1

B. 16

C. 23

D. 40

Answer: B. 16

11. The mass contribution of hydrogen in NaOH is:

A. 1

B. 8

C. 16

D. 23

Answer: A. 1

12. If the volume of a solution increases while moles remain constant, molarity:

A. Increases

B. Decreases

C. Becomes zero immediately

D. Remains necessarily constant

Answer: B. Decreases

13. If the amount of solute increases while volume remains constant, molarity:

A. Increases

B. Decreases

C. Remains unchanged

D. Becomes zero

Answer: A. Increases

14. Which quantity is used in the numerator of the molarity formula?

A. Volume

B. Moles

C. Density

D. Temperature

Answer: B. Moles

15. Which quantity is used in the denominator of M = n/V?

A. Mass

B. Moles

C. Volume in litres

D. Molar mass

Answer: C. Volume in litres

16. 1 L is equal to:

A. 10 mL

B. 100 mL

C. 500 mL

D. 1000 mL

Answer: D. 1000 mL

17. If 0.125 mol NaOH is present in 0.450 L solution, its molarity is:

A. 0.0278 M

B. 0.278 M

C. 2.78 M

D. 27.8 M

Answer: B. 0.278 M

18. Molarity is based on the volume of:

A. Solvent only

B. Solution

C. Solute only

D. Container

Answer: B. Solution

19. The unit mol L⁻¹ can also be written as:

A. M

B. m

C. N only

D. kg

Answer: A. M

20. A 1 M solution contains:

A. 1 mole solute per litre solution

B. 1 gram solute per litre

C. 1 mole solvent per litre

D. 1 kg solute per litre

Answer: A. 1 mole solute per litre solution

21. Which formula can directly calculate molarity from mass?

A. M = mass × molar mass / volume

B. M = mass / (molar mass × volume in L)

C. M = volume / mass

D. M = molar mass / mass

Answer: B. M = mass / (molar mass × volume in L)

22. The given solution contains 0.125 mol NaOH. This quantity represents:

A. Mass

B. Number of moles

C. Volume

D. Density

Answer: B. Number of moles

23. If the same 5 g NaOH were dissolved to make 1 L solution, the molarity would be:

A. 0.0125 M

B. 0.125 M

C. 1.25 M

D. 12.5 M

Answer: B. 0.125 M

24. If the same 5 g NaOH were dissolved to make 0.225 L solution, the molarity would be:

A. 0.278 M

B. 0.556 M

C. 1.11 M

D. 2.22 M

Answer: B. 0.556 M

25. Molarity changes with temperature mainly because:

A. Number of atoms changes

B. Volume of solution may change

C. Molar mass changes

D. Atomic number changes

Answer: B. Volume of solution may change

26. Which is NOT needed directly to calculate molarity from mass?

A. Mass of solute

B. Molar mass

C. Volume of solution

D. Atomic number of solvent

Answer: D. Atomic number of solvent

27. The molarity calculated for the given solution to three significant figures is:

A. 0.278 M

B. 0.28 M

C. 2.78 M

D. 27.8 M

Answer: A. 0.278 M

28. In a dilution process, if moles remain constant and volume increases, concentration:

A. Increases

B. Decreases

C. Becomes infinite

D. Always remains unchanged

Answer: B. Decreases

29. The value 0.278 M means approximately:

A. 0.278 mol NaOH per litre solution

B. 0.278 g NaOH per litre

C. 2.78 mol NaOH per litre

D. 278 mol NaOH per litre

Answer: A. 0.278 mol NaOH per litre solution

30. The correct final answer for the given problem is:

A. 0.0278 M

B. 0.278 M

C. 2.78 M

D. 27.8 M

Answer: B. 0.278 M

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