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Ghella [55]
3 years ago
15

(25 points) A certain isotope of technetium has a half-life of 8 hours. How much of a 40 gram sample will be left after 16 hours

?
A. 10 grams
B. 40 grams
C. 5 grams
D. 20 grams
Chemistry
1 answer:
gtnhenbr [62]3 years ago
6 0

Answer:

A) 10 grams

Explanation:

16 hours = 2 half lives

This means that the number is divided in half twice.

40/2 = 20

20/2 = 10

I hope this helps!! :)

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A student needed to make a 3 g/L NaCl solution. The student weighed 3 g of NaCl in a beaker and measured 1 L of water in a 1L vo
hoa [83]

Answer:

The answer is in the explanation.

Explanation:

A solution is defined as the <em>homogeneous mixture </em>of a solute (In this case, NaCl) and the solvent (water).

To prepare 1L of the solution, the student can weigh the 3g of NaCl in the volumetric flask but need to add slowly water to dissolve the NaCl (That is very soluble in water). When all NaCl is dissolved the student must transfer the solution to the 1L volumetric flask. Then, you must add more water to the beaker until "Clean" all the solute of the beaker to transfer it completely to the volumetric flask.

8 0
2 years ago
Explain why it is necessary to balance chemical equations in terms of maintaining equilibrium. How can you tell when a chemical
LUCKY_DIMON [66]

Answer:

See explanation.

Explanation:

Hello,

In this case, we say that chemical reactions are governed by the law of conservation of mass, which states that matter cannot be neither created nor destroyed by transformed, for that reason, we need to balance chemical reactions in order to ensure all the atoms to be in the same quantity at both reactants and products.

Moreover, equilibrium is defined as such condition at which the concentration of both reactants and products stop changing over the time so they become constant as well as their null reaction rate.

A widely acknowledged reaction is the HABER one which consists on the synthesis of ammonia by using elemental nitrogen and hydrogen:

N_2(g)+3H_2(g)\rightleftharpoons 2NH_3(g)

In such reaction, we have two nitrogens at both reatants and products and six hydrogens at at both reatants and products for us to obey the law of conservation of mass. Furthermore, as the time goes by, nitrogen reacts with hydrogen, nonetheless, they do not react indefinitely, they have a limit that is equilibrium, so their moles stop being consumed and remain unchanged as well as the produced moles of ammonia.

Best regards.

7 0
3 years ago
If a compound contains a poly atomic ion then what type of compound is it A. Convalent Compound B. Ionic Compound
den301095 [7]

Answer:

B. Ionic Compound

Explanation:

An ionic compound is that compound which contains a positively charged ion called CATION and a negatively charged ion called ANION. The cation loses or transfers electrons to the anion, hence, making the former (cation) positive and the latter (anion) negative.

A polyatomic ion is an ion that contains more than one type of atom e.g OH-, NO3²-, CO3²- etc. A polyatomic ion usually has an overall charge formed from the charges of the individual atoms that makes it up. For example, in OH-, the overall charge is -1.

Since a polyatomic ion can have an overall positive or negative charge, it must enter a reaction with another ion that complements it i.e. a negative polyatomic ion will react with a positive ion to neutralize its charge. Hence, this forms an IONIC COMPOUND. This is why most compounds with polyatomic ions are IONIC COMPOUNDS.

For example, CaCO3 is an ionic compound formed when Ca²+ (cation) reacts with the polyatomic anion: CO3²-

5 0
3 years ago
What is the molarity of a NaOH solution if 28.2 mL of a 0.355 M H2SO4 solution is required to neutralize a 25.0-mL sample of the
Verdich [7]

Answer:

[NaOH} = 0.4 M

Explanation:

In a reaction of neutralization, we determine the equivalence point of the titration. In this case, we have a strong base and a strong acid.

(H₂SO₄, is considered strong, but the first deprotonation is weak)

2NaOH  +  H₂SO₄  →  Na₂SO₄  + 2H₂O

As we have 2 protons in the acid, we need 2 OH⁻ from the base to form 2 molecules of water.

In the equivalence point we know mmoles of base = mmoles of acid

Let's finish the excersise with the formula

25 mL . M NaOH = 28.2 mL  .  0.355M

M NaOH = (28.2 mL  .  0.355M) / 25 mL → 0.400

8 0
3 years ago
Explain how metallic bonding causes metals to conduct electricity?
astra-53 [7]
In a metallic bond, atoms of the metal are surrounded by a constantly moving "sea of electrons". This moving sea of electrons enables the metal to conduct electricity and move freely among the ions.
3 0
3 years ago
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