Question

1. an iphone weighs 129 g. 0.67% of that mass is lithium (li). how many lithium atoms are in the phone?
2. a sample of carbon weighs 0.20 g and a sample of platinum (pt) weighs 2.0 g. which sample contains more atoms? (show all your work.)

Explanation:

Question 3

Step 1: Calculate mass of Li

First, find the mass of lithium in the iPhone. The total mass of the iPhone is 129 g, and 0.67% of that is Li. So, mass of Li = \( 129\ g\times\frac{0.67}{100} \)
\( 129\times0.0067 = 0.8643\ g \)

Step 2: Calculate moles of Li

Molar mass of Li is approximately 6.94 g/mol. Moles of Li = \( \frac{\text{mass of Li}}{\text{molar mass of Li}}=\frac{0.8643\ g}{6.94\ g/mol} \approx 0.1245\ mol \)

Step 3: Calculate number of atoms

Using Avogadro's number (\( 6.022\times 10^{23}\ atoms/mol \)), number of Li atoms = moles × Avogadro's number
\( 0.1245\ mol\times6.022\times 10^{23}\ atoms/mol \approx 7.498\times 10^{22}\ atoms \)

To determine which sample has more atoms, we calculate the number of moles of each element and then the number of atoms (since number of atoms = moles × Avogadro's number, the sample with more moles will have more atoms).

Step 1: Calculate moles of Carbon (C)

Molar mass of C is 12.01 g/mol. Moles of C = \( \frac{\text{mass of C}}{\text{molar mass of C}}=\frac{0.20\ g}{12.01\ g/mol} \approx 0.0167\ mol \)

Step 2: Calculate moles of Platinum (Pt)

Molar mass of Pt is 195.08 g/mol. Moles of Pt = \( \frac{\text{mass of Pt}}{\text{molar mass of Pt}}=\frac{2.0\ g}{195.08\ g/mol} \approx 0.01025\ mol \)

Step 3: Compare moles

Moles of C (≈0.0167 mol) is greater than moles of Pt (≈0.01025 mol). Since number of atoms is proportional to moles (atoms = moles × \( 6.022\times 10^{23} \)), the carbon sample has more atoms.

Answer:

Approximately \( 7.5\times 10^{22} \) lithium atoms (or more precisely around \( 7.5\times 10^{22} \))

Question 4