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3 years ago

Write a speech aimed at year 7 to explain why some metals lose their shine over time but gold does not.

1 answer:

8 0

The reason of why some metals lose their shine over time but the gold does not is so simple that's because the corrosion and tarnish processes. Metals donate electrons when exposed to atmosphere and tends to form oxide. and when the metal donate electrons the oxygen tends to accept this electrons and fill up its shell and form oxide and the metal lose its shine.when the oxide film contact with an aqueous medium metal oxide pairs with H2O and form rust.

But gold is a noble metal (like platinum and silver), it remains stable in its pure form and doesn't donate electrons so, no loss electrons and the oxide don't happen at all. So the gold is known for its resistance to oxidation. As the noble metals have a very low reaction rate with oxygen, So there is no rusting as the rusting is the result of the reaction of the oxygen with the metals.So there is no tarnish appears. that's why the gold doesn't lose its shine and keeps its pure form.

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B. An equal amount of protons and electrons

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At the normal melting point of NaCl, 801 degrees C, its enthalpy of fusion is 28.8 kJ / mol. The density of the solid is 2.165 g

melisa1 [442]

Answer: The increase in pressure is 0.003 atm

Explanation:

To calculate the final pressure, we use the Clausius-Clayperon equation, which is:

$\ln(\frac{P_2}{P_1})=\frac{\Delta H}{R}[\frac{1}{T_1}-\frac{1}{T_2}]$

where,

$P_1$ = initial pressure which is the pressure at normal boiling point = 1 atm

$P_2$ = final pressure = ?

$\Delta H$ = Enthalpy change of the reaction = 28.8 kJ/mol = 28800 J/mol (Conversion factor: 1 kJ = 1000 J)

R = Gas constant = 8.314 J/mol K

$T_1$ = initial temperature = $801^oC=[801+273]K=1074K$

$T_2$ = final temperature = $(801+1.00)^oC=802.00=[802+273]K=1075K$

Putting values in above equation, we get:

$\ln(\frac{P_2}{1})=\frac{28800J/mol}{8.314J/mol.K}[\frac{1}{1074}-\frac{1}{1075}]\\\\\ln P_2=3\times 10^{-3}atm\\\\P_2=e^{3\times 10^{-3}}=1.003atm$

Change in pressure = $P_2-P_1=1.003-1.00=0.003atm$

Hence, the increase in pressure is 0.003 atm

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3 years ago

In an atomic model that includes a nucleus, positive charge is

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Because protons are positively charged and neutrons have no charge then it is safe to say that such an atomic model would have the positive charge concentrated in the center of an atom (option d).

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Answer: Option (c) is the correct answer.

Explanation:

Backbone in a nucleic acids strand is made up of sugar molecules attached with phosphodiester bond.

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Thus, we can conclude that the backbone in a nucleic acids strand is called sugar backbone.

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2 years ago

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