All categories

3 years ago

Calcium-45 has a half-life of 162.7 days. if four half-lives have elapsed, how much time has passed?

Chemistry

2 answers:

enyata [817]3 years ago

7 0

Answer:

650.8 days

Explanation:

if the half-life is 162.7 days and the number of half-life days has elapsed 4 times.

To know the number of days that have passed we must multiply the half-life by 4

$4(162.6)= 650.8 days$

stiv31 [10]3 years ago

3 0

Half-life is the time required for a quantity to reduce to half its initial value. If four half-lives have elapsed for calcium-45, then it would be 4x162.7 = 650.8 days have passed. Hope this answers the question. Have a nice day. Feel free to ask more questions.

You might be interested in

Phosphoric acid is a triprotic acid with the following pKa values:pKa1=2.148, pKa2=7.198, pKa3=12.375You wish to prepare 1.000 L

laila [671]

Answer:

NaH₂PO₄ = 1.876 g

Na₂HPO₄ = 4.879 g

Combinations: H₃PO₄ and Na₂HPO₄; H₃PO₄ and Na₃HPO₄

Explanation:

To have a buffer at 7.540, the acid must be in it second ionization, because the buffer capacity is pKa ± 1. So, we must use pKa2 = 7.198

The relation bewteen the acid and its conjugated base (ion), is given by the Henderson–Hasselbalch equation:

pH = pKa + log[A⁻]/[HA], where [A⁻] is the concentration of the conjugated base, and [HA] the concentration of the acid. Then:

7.540 = 7.198 + log[A⁻]/[HA]

log[A⁻]/[HA] = 0.342

[A⁻]/[HA] = $10^{0.342}$

[A⁻]/[HA] = 2.198

[A⁻] = 2.198*[HA]

The concentration of the acid and it's conjugated base must be equal to the concentration of the buffer 0.0500 M, so:

[A⁻] + [HA] = 0.0500

2.198*[HA] + [HA] = 0.0500

3.198*[HA] = 0.0500

[HA] = 0.01563 M

[A⁻] = 0.0500 - 0.01563

[A⁻] = 0.03436 M

The mix reaction is

NaH₂PO₄ + Na₂HPO₄ → HPO₄⁻² + 3Na + H₂PO₄⁻

The second ionization is:

H₂PO₄⁻ ⇄ HPO₄⁻² + H⁺

So, H₂PO₄⁻ is the acid form, and its concentration is the same as NaH₂PO₄, and HPO₄⁻² is the conjugated base, and its concentration is the same as Na₂HPO₄ (stoichiometry is 1:1 for both).

So, the number of moles of these salts are:

NaH₂PO₄ = 0.01563 M * 1.000 L = 0.01563 mol

Na₂HPO₄ = 0.03436 M* 1.000 L = 0.03436 mol

The molar masses are, Na: 23 g/mol, H: 1 g/mol, P: 31 g/mol, and O = 16 g/mol, so:

NaH₂PO₄ = 23 + 2*1 + 31 + 4*16 = 120 g/mol

Na₂HPO₄ = 2*23 + 1 + 31 + 4*16 = 142 g/mol

The mass is the number of moles multiplied by the molar mass, so:

NaH₂PO₄ = 0.01563 mol * 120 g/mol = 1.876 g

Na₂HPO₄ = 0.03436 mol * 142 g/mol = 4.879 g

To prepare this buffer, it's necessary to have in solution the species H₂PO₄⁻ and HPO₄⁻², so it can be prepared for mixing the combination of:

H₃PO₄ and Na₂HPO₄ (the acid is triprotic so, it will form the H₂PO₄⁻ , and the salt Na₂HPO₄ will dissociate in Na⁺ and HPO₄²⁻);

H₃PO₄ and Na₃HPO₄ (same reason).

The other combinations will not form the species required.

8 0

3 years ago

Zinc reacts with hydrochloric acid according to the reaction equation Zn ( s ) + 2 HCl ( aq ) ⟶ ZnCl 2 ( aq ) + H 2 ( g ) How ma

Katen [24]

Answer: 12.0 milliliters of 6.50 M HCl ( aq ) are required to react with 2.55 g Zn.

Explanation:

moles = $\frac{\text {given mass}}{\text {Molar mass}}$

moles of zinc = $\frac{2.55g}{65.38g/mol}=0.0390moles$

The balanced chemical equation is :

$Zn(s)+2HCl(aq)\rightarrow ZnCl_2(aq)+H_2(g)$

According to stoichiometry:

1 mole of zinc reacts with = 2 moles of HCl

Thus 0.0390 moles of zinc reacts with = $\frac{2}{1}\times 0.0390=0.0780$ moles of HCl

To calculate the volume for given molarity, we use the equation:

$\text{Molarity of the solution}=\frac{\text{Moles of solute}\times 1000}{\text{Volume of solution in ml}}$ .....(1)

Molarity of $HCl$ solution = 6.50 M

Volume of solution = ?

Putting values in equation 1, we get:

$6.50M=\frac{0.0780\times 1000}{\text{Volume of solution in ml}}$

${\text{Volume of solution in ml}}=12.0ml$

Thus 12.0 ml of 6.50 M HCl ( aq ) are required to react with 2.55 g Zn

3 0

3 years ago

Que diferencia hay entre drogas estimuladoras depresoras y perturbadoras del sistema nervioso

12345 [234]

Answer:

Las drogas estimulantes son un grupo de medicamentos que tienen un efecto estimulante mental y físico en humanos y animales, estimulando y dando energía al paciente. Ejemplos de psicoestimulantes son cafeína, efedrina, anfetaminas y metilfenidato. Estos se usan en pequeñas dosis para, entre otras cosas, mejorar la atención del paciente y la capacidad de planificación, permitiendo un mayor y mejor rendimiento de la persona durante sus actividades diarias.

A su vez, un depresor es una sustancia que paraliza las funciones del sistema nervioso central, siendo las pastillas para dormir y los sedantes los depresores mas comunes. La acción de los sedantes se basa en su capacidad para activar los mediadores del sistema nervioso central, especialmente el ácido gamma-aminobutírico, causando en el paciente una sensación que puede ir desde la tranquilidad y relajación hasta un estado de somnolencia o incluso la propia inducción al sueño.

Por último, las drogas perturbadoras del sistema nervioso incluyen LSD, cannabis o la cocaína. Algunos efectos típicos son cambios en la visión y el oído, alucinaciones, confusión de sentidos, fuertes experiencias de belleza, disolución del yo y un sentido de unidad, experiencias religiosas y confrontaciones con el subconsciente. Este tipo de drogas son en su gran mayoría ilegales, y no forman parte de tratamientos médicos autorizados.

3 0

3 years ago

What is the pH of .0003 M of NaOH

s344n2d4d5 [400]

We are given that the concentration of NaOH is 0.0003 M and are asked to calculate the pH

We know that NaOH dissociates by the following reaction:

NaOH → Na⁺ + OH⁻

Which means that one mole of NaOH produces one mole of OH⁻ ion, which is what we care about since the pH is affected only by the concentration of H⁺ and OH⁻ ions

Now that we know that one mole of NaOH produces one mole of OH⁻, 0.0003M NaOH will produce 0.0003M OH⁻

Concentration of OH⁻ (also written as [OH⁻]) = 3 * 10⁻⁴

pOH of the solution:

pOH = -log[OH⁻] = -log(3 * 10⁻⁴)

pOH = -0.477 + 4

pOH = 3.523

pH of the solution:

We know that the sum of pH and pOH of a solution is 14

pH + pOH = 14

pH + 3.523 = 14 [subtracting 3.523 from both sides]

pH = 10.477

8 0

3 years ago

Omg GUYS I NEED HELPPP

Ilia_Sergeevich [38]

27) Partial pressure of oxygen: 57.8 kPa

29) Final volume: 80 mL

30) Final volume: 8987 L

31) Due to property of water of being polar, ice floats on water

Explanation:

27)

In a mixture of gases, the total pressure of the mixture is the sum of the partial pressures:

$p_T = p_1 + p_2 + ... + p_N$

In this problem, the mixture contains 3 gases (helium, carbon dioxide and oxygen). We know that the total pressure is

$p_T=201.4 kPa$

We also know the partial pressures of helium and carbon dioxide:

$P_{He}=125.4 kPa\\P_{CO_2}=18.2 kPa$

The total pressure can be written as

$p_T=p_{He}+p_{CO_2}+p_{O_2}$

where $p_{O_2}$ is the partial pressure of oxygen. Therefore, we find

$p_{O_2}=p_T-p_{He}-p_{CO_2}=201.4-125.4-18.2=57.8 kPa$

29)

Assuming that the pressure of the gas is constant, we can apply Charle's law, which states that:

"For an ideal gas at constant pressure, the volume of the gas is proportional to its absolute temperature"

Mathematically,

$\frac{V}{T}=const.$

where

V is the volume of the gas

T is the Kelvin temperature

We can re-write it as

$\frac{V_1}{T_1}=\frac{V_2}{T_2}$

Here we have:

$V_1 = 42 mL$ (initial volume)

$T_1=-89^{\circ}C+273=184 K$ is the initial temperature

$T_2=77^{\circ}C+273=350 K$ is the final temperature

Solving for V2, we find the final volume:

$V_2=\frac{V_1 T_2}{T_1}=\frac{(42)(350)}{184}=80 mL$

30)

For this problem, we can use the equation of state for ideal gases, which can be written as

$\frac{p_1 V_1}{T_1}=\frac{p_2 V_2}{T_2}$

where in this problem:

$p_1 = 102.3 kPa$ is the initial pressure

$V_1=1975 L$ is the initial volume

$T_1=25^{\circ}C+273=298 K$ is the initial temperature

$p_2=21.5 kPa$ is the final pressure

$T_2=12^{\circ}C+273=285 K$ is the final temperature

And solving for V2, we find the final volume of the balloon:

$V_2=\frac{p_1 V_1 T_2}{p_2 T_1}=\frac{(102.3)(1975)(285)}{(21.5)(298)}=8987 L$

31)

A molecule of water consists of two atoms hydrogen bond with an atom of oxygen ( $H_2 O$ ) in a covalent bond.

While the molecul of water is overall neutral, due to the higher electronegativity of the oxygen atom, electrons are slightly shifted towards the oxygen atom; as a result, there is a slightly positive charge on the hydrogen side, and a slightly negative charge on the oxygen side (so, the molecules is said to be polar).

As a consequence, molecules of water attract each other, forming the so-called "hydrogen bonds".

One direct consequence of the polarity of water is that ice floats on liquid water.

Normally, for every substance on Earth, the solid state is more dense than the liquid state. However, this is not true for water, because ice is less dense than liquid water.

This is due to the polarity of water. In fact, when the temperature of water is decreased to freezing point and water becomes ice, the hydrogen bondings "force" the molecules to arrange in a lattice structure, so that the molecules become more spaced when they turn into solid state. As a result, ice occupies more volume than water, and therefore it is less dense, being able to float on water.

Learn more about ideal gases:

brainly.com/question/9321544

brainly.com/question/7316997

brainly.com/question/3658563

#LearnwithBrainly

4 0

3 years ago