Answer:
a) a0 was 46.2 grams
b) It will take 259 years
c) The fossil is 1845 years old
Explanation:
<em>An unknown radioactive substance has a half-life of 3.20hours . If 46.2g of the substance is currently present, what mass A0 was present 8.00 hours ago?</em>
A = A0 * (1/2)^(t/h)
⇒ with A = the final amount = 46.2 grams
⇒ A0 = the original amount
⇒ t = time = 8 hours
⇒ h = half-life time = 3.2 hours
46.2 = Ao*(1/2)^(8/3.2)
Ao = 261.35 grams
<em>Americium-241 is used in some smoke detectors. It is an alpha emitter with a half-life of 432 years. How long will it take in years for 34.0% of an Am-241 sample to decay?</em>
t = (ln(0.66))-0.693) * 432 = 259 years
It will take 259 years
<em>A fossil was analyzed and determined to have a carbon-14 level that is 80% that of living organisms. The half-life of C-14 is 5730 years. How old is the fossil?</em>
<em />
t = (ln(0.80))-0.693) * 5730 = 1845
The fossil is 1845 years old
Answer:
2H⁺(aq) + Sr(OH)₂(s) ⟶ Sr²⁺(aq) + 2H₂O(ℓ)
Explanation:
You aren't dumb. You just need more time to learn the concepts.
There are three steps you must follow. You must write the:
- Molecular equation
- Ionic equation
- Net ionic equation
1. Molecular equation
2HBr + Sr(OH)₂ ⟶ SrBr₂ + 2H₂O
To predict the states of the substances, we must remember some solubility rules:
- HBr is a strong acid. It dissociates completely in water.
- Most hydroxides are only slightly soluble. Unless the solution is quite dilute, I would write their states in water as "(s)", i.e., a suspension of the solid in water.
- Salts containing Br⁻ are generally soluble.
Acids and bases react to give salts and water.
Thus, the molecular equation is
2HBr(aq) + Sr(OH)₂(s) ⟶ SrBr₂(aq) + 2H₂O(ℓ)
B. Ionic equation
You write all the soluble substances as ions.
2H⁺(aq)+ 2Br⁻(aq) + Sr(OH)₂(s) ⟶ Sr²⁺(aq) + 2Br⁻(aq) + 2H₂O(ℓ)
C. Net ionic equation
To get the net ionic equation, you cancel the ions that appear on each side of the ionic equation.
2H⁺(aq) + <u>2Br⁻(aq)</u> + Sr(OH)₂(s) ⟶ Sr²⁺(aq) + <u>2Br⁻(aq)</u> + 2H₂O(ℓ)
The net ionic equation is
2H⁺(aq) + Sr(OH)₂(s) ⟶ Sr²⁺(aq) + 2H₂O(ℓ)
Answer:
c) neutrons and protons
Explanation:
The nucleus of the atom contains only neutrons and protons. Electrons are not in the nucleus but outside the nucleus in 'atomic orbitals'.
<u>Given:</u>
Concentration of NaClO = 0.037 M
ka (HClO) = 4.0*10⁻⁸
<u>To determine:</u>
The pH of the NaClO solution
<u>Explanation:</u>
The hydrolysis of the weak base can be represented by the ICE table shown below-
ClO- + H2O ↔ HClO + OH-
Initial 0.037M 0 0
Change -x +x +x
Equilibrium (0.037-x) x x
kb = kw/ka = [HClO][OH-]/[ClO-]
10⁻¹⁴/4*10⁻⁸ = x²/(0.037-x)
x = [OH-] = 9.62*10⁻⁵
p[OH-] = -log[OH-] = -log [9.62*10⁻⁵] = 4.02
pH = 14-p[OH-] = 14 - 4.02 = 9.98
Ans: pH of the solution is 9.98