Practice 1-3 Chem

A metal weighs 9.25 g. In water, it raises the level from 21.25 mL to 26.47 mL. What's its density?

1.77 g/mL — Volume = 26.47−21.25 = 5.22 mL; d = 9.25 g ÷ 5.22 mL = 1.77 g/mL

How many sig figs are in 0.001500 g?

4 — leading zeros never count; trailing zeros after a decimal point DO count (1,5,0,0)

(3.335 × 5.400) + 0.940 = ? How many sig figs?

Four — multiply first (18.01, 4 sig figs), then add (18.01+0.940=18.95, limited by fewest decimal places)

Convert 990. kg to mg.

9.90 × 10⁸ mg — kg→g (×1000) then g→mg (×1000)

Convert 45 liters to m³.

4.5 × 10⁻² m³ — 1 L = 10⁻³ m³

Which is a PHYSICAL property: Na reacts with Cl2 / Hg is a silvery liquid / Cu rusts / CH4 is flammable?

Mercury is a silvery liquid at room temp — observed without changing chemical composition

The mass number of an atom equals the sum of:

Protons + neutrons (NOT electrons)

"Matter is neither created nor destroyed" is which law?

Law of Conservation of Mass

Which is the smallest subatomic particle: neutron, electron, proton, alpha particle?

Electron — ~2000x lighter than protons/neutrons

Element X: X-45 (44.8776 amu, 32.88%), X-47 (46.9443 amu, 67.12%). Find atomic mass.

46.26 amu — (0.3288×44.8776)+(0.6712×46.9443)

For an atom with mass number 25, atomic number 12 (neutral): find p, n, e-

P=12, N=13 (25−12), e⁻=12

How many phosphorus atoms in 158 kg P? (molar mass ≈30.97 g/mol)

3.07 × 10²⁷ atoms — convert kg→g→mol→atoms using Avogadro's number

Which element is a halogen: Ge, Cl, Co, Kr?

Cl — halogens are Group 7A (F, Cl, Br, I, At)

Species with p⁺=12, n°=14, e⁻=10 — what is it?

Mg²⁺ — 12 protons = magnesium; lost 2 electrons (12−10=+2 charge)

Which exists as a polyatomic molecular element: Ne, C, P, Ca?

Phosphorus — exists naturally as P₄

A covalent bond is best described as:

Sharing of electrons between two or more nonmetals (not transfer — that's ionic)

Write the formula for strontium perchlorate.

Sr(ClO₄)₂ — Sr²⁺ needs 2 ClO₄⁻ (perchlorate) to balance charge

Name P₄O₁₀ using molecular naming rules.

Tetraphosphorus decoxide — Greek prefixes for both elements, no Roman numerals

What is the chemical formula for sulfurous acid?

H₂SO₃(aq) — from sulfite (SO₃²⁻, "-ite") → "-ous acid"

Find mass % of N in C₁₄H₁₉NO₂ (N=14.01 amu, molar mass ≈233.3 g/mol)

6.00% — (14.01 ÷ 233.3) × 100%

Mass of 9.44 × 10²⁴ molecules of NO₂? (molar mass = 46.01 g/mol)

721 g — molecules→moles (÷6.022×10²³)→grams (×46.01)

How much Ca in 50.0 g CaF₂? (molar mass 78.074 g/mol, Ca=40.078 g/mol)

25.7 g — mass % Ca = 51.33%, then 50.0 g × 0.5133

40.00 g alcohol (C,H,O) combusts to 76.40 g CO₂ + 46.96 g H₂O. Empirical formula?

C₂H₆O — convert CO₂/H₂O to mol C/H, find mol O by mass difference, reduce to whole-number ratio

Compound: molar mass 122.11 g/mol, empirical formula C₂H₅O₂ (mass ≈61.05 g/mol). Molecular formula?

C₄H₁₀O₄ — n = 122.11÷61.05 ≈ 2, multiply subscripts by 2

Difference between "-ate" and "-ite" endings (e.g. NO₃⁻ vs NO₂⁻)?

"-ate" has one MORE oxygen than "-ite" (nitrate vs nitrite)

The Law of Definite Proportions states:

All samples of a compound have the same fixed mass ratio of elements, regardless of source

Rutherford's gold foil experiment proved atoms have:

A tiny, dense, positively charged nucleus with mostly empty space around it