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2 years ago

Is water going from liquid to solid a physical or chemical change and why

1 answer:

6 0

It would be a physical change. It’s still water just in a different physical form. If it was a chemical change, it would no longer be water. For example, when the ice melts back into water...it’s still water.

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List three conditions for separating crude oil constituents pls someone help me out

Alborosie

Answer:

All refineries have three basic steps: separation, conversion and treatment. During the separation process, the liquids and vapors separate into petroleum components called factions based on their weight and boiling point in distillation units.

Explanation:

4 0

2 years ago

A certain element forms an ion with 36 electrons and a charge of +2. identify the element. express your answer as a chemical sym

blsea [12.9K]

The element is Sr (strontium)

strontium is in atomic number 38 in the periodic table. Strontium has 2.8.8.8.8.2

it loses two electrons to become stable hence it has a charge of 2+. when strontium loses two electron it form ion with 36 electrons

6 0

3 years ago

What two atoms are held together by a covalent bond in NaHCO3

gtnhenbr [62]

Answer: covalent bond is the force of attraction that holds together two atoms that share a pair of valence electrons. Covalent bonds form only between atoms of nonmetals. The two atoms that are held together in a covalent bond may be atoms of the same element or different elements.

Explanation:

8 0

2 years ago

A tank contains 200 gallons of water in which 300 grams of salt is dissolved. A brine solution containing 0.4 kilograms of salt

Nadusha1986 [10]

Answer:

<h3>Therefore, after long period of time 80kg of salt will remain in tank</h3>

Explanation:

given amount of salt at time t is A(t)

initial amount of salt =300 gm =0.3kg

=>A(0)=0.3

rate of salt inflow =5*0.4= 2 kg/min

rate of salt out flow =5*A/(200)=A/40

rate of change of salt at time t , dA/dt= rate of salt inflow- ratew of salt outflow

$dA/dt=2-(A/40)\\\\dA=2dt-(A/40)dt\\\\dA+(A/40)dt=2dt$

integrating factor

$=e^{\int\limits (1/40) \, dt}$

integrating factor $=e^{(1/40)t}$

multiply on both sides by $=e^{(1/40)t}$

$dAe^{(1/40)t}+(A/40)e^{(1/40)t} dt =2e^{(1/40)t}t\\\\(Ae^{(1/40)t})=2e^{(1/40)t}t$

integrate on both sides

$\int\limits(Ae^{(1/40)t})=\int\limits2e^{(1/40)t}dt\\\\(Ae^{(1/40)t})=2*40e^{(1/40)t}+C\\\\A=80+(C/e^{(1/40)t})\\\\A(0)=0.3\\\\0.3=80+(C/e^{(1/40)t}^*^0)\\\\0.3=80+(C/1)\\\\C=0.3-80\\\\C=-79.7\\\\A(t)=80-(79.7/e^{(1/40)t})$

after long period of time means t - > ∞

${t \to \infty}\\\\ \lim_{t \to \infty} A_t \\\\ \lim_{t \to \infty} (80)-(79/{e^{(1/40)t}}\\\\=80-(0)\\\\=80$

<h3>Therefore, after long period of time 80kg of salt will remain in tank</h3>

6 0

2 years ago

What is the net charge of the peptide arg-ala-phe-leu at ph 8?

adell [148]

The structure of this oligopeptide is attached:

It consists of arginine - alanine - phenylalanine and leucine

From the picture we can see that N terminus charge is +1
Also Arginine is considered as basic amino acid with charge +1
C terminus charge is -1

At pH = 8, the whose pKa are less than pH will be deprotonated and the net charge will be +1

So the net charge of this oligopeptide is +1 at pH = 8

3 0

2 years ago