A sample of carbon-12 has a mass of 3.0 g. Which expression gives the number of atoms in the sample? (NA is the symbol of the Avogadro costant)
Correct answer: B. 0.25 NA
- A. 0.0030 NA
- B. 0.25 NA
- C. 3.0 NA
- D. 4.0 N A
Explanation
The number of atoms in a sample can be determined by first calculating the number of moles using the formula: Number of moles = Mass / Molar mass. For carbon-12, the molar mass is 12 g/mol, so the number of moles in a 3.0 g sample is 3/12 = 0.25 moles. The number of atoms is then found by multiplying the number of moles by Avogadro's constant (NA), which gives 0.25 NA. Therefore, option B is correct.Option A incorrectly calculates the moles, leading to a wrong number of atoms. Option C incorrectly assumes that mass in grams is equivalent to moles, and Option D makes an incorrect calculation of moles.
This question appeared on the ETEA MDCAT 2013 paper, which you can sit online with every answer explained.
Report an error
The more specific you are, the faster it gets fixed. A source beats an opinion.
Prefer email? [email protected]
About Moles and Avogadro's Number
The mole connects the microscopic number of particles with measurable mass, using Avogadro's number, 6.022 × 10²³ particles per mole. Questions involve molar mass, conversion between mass, moles and particles, percentage composition, empirical and molecular formulas, and distinguishing atoms, molecules, ions and formula units.
Practise Fundamental Concepts of Chemistry
894 free Fundamental Concepts of Chemistry MCQs from Chemistry, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Discussion
Stuck on an option, or know a faster way to get there? Ask or explain it here.
No comments yet. Be the first to explain this one.
Exams that ask Chemistry questions like this
Chemistry is on 14 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
More Moles and Avogadro's Number questions
How many molecules are present in 0.20 g of Hydrogen gas? Select the correct option.
One mole is the amount of substance that contains as many elementary entities as contained in:
1 amu is equal to 1.661 x 10^-24g, then 1.0 g will be equal to:
Equal volume of different gases under same condition of temperature and pressure contain the same number of particles. The above statement is of:
What is the number of hydrogen atoms in 5 moles of water?
How many oxygen atoms are present in 278g of Hydrated Ferrous Sulphate?(FeSO4.7Hz 0 = 278 any)