Salt lowers the freezing point and melting point of water/ice. Ice forms when water freezes and becomes 0 degree Celsius. When salt is added to ice, it dissolves into the liquid water within the ice and lowers that temperature and freezing point. “A 10-percent salt solution freezes at -6 Celsius, and a 20-percent solution freezes at -16 C.”
If one has ever watched salt melting ice, you can see the dissolving process happen, as the salt dissolves in the water and spreads out from the point first melted. Although, if the temperature of the roadway is lower than -9 Celsius or so, then the salt really won't have any affect the solid salt cannot get into the structure of the solid water to start the dissolving process.
Effect of Sand on Ice Sand can melt ice if it is heated naturally from the sun or a warm temperature, just like all other substances that is at a higher temperature than ice. The actual texture of sand does not cause ice to melt. Sand, unless it is at a higher temperature than the ice, it would not melt.
Effect of Sugar on Ice Fact: Sugar, and anything else that is able to dissolve in water, will melt ice. Like salt, sugar melts ice by lowering water's melting and freezing points. When sugar is added onto ice, it dissolves and interferes with the water molecules, which need to bind to ice crystals in order to freeze. Sugar’s presence needs the temperature to be much colder before the water molecules come into contact with ice crystals.
While sugar will melt ice, it still isn’t as effective as salt, which breaks down into sodium and chloride ions. When one molecule of salt dissolves, it adds two components to the solution, providing more interference in preventing water molecules from freezing.
Effect of Flour on Ice “If you put flour in water, you make pancake batter which freezes at about the same temperature as water. So it won't melt ice at all.”
Conclusion: Sugar and salt lowers the freezing/melting pointing of water/ice,therefore making the ice melt. Although salt is more efficient when one molecule of salt dissolves, it adds two components to the solution, providing more interference in preventing water molecules from freezing. Sand melts ice by providing traction and absorbing heat and being at a higher temperature than the ice, hence, melting it. Flour has no effect on ice, and may even serve as an insulator from the higher temperature that surrounds the ice.
The correct answer is: d. The pKa of the chosen buffer should be close to the optimal pH for the biochemical reaction.
Explanation:
The buffer resist or maintain the change in pH in case of Acid or basic addition to the solution. The buffer capacity should be within one or two pH units when compared to the optimal pH.
Thus it is important to select a buffer with pKa close to the optimum pH of the reaction because the ability for the buffer to maintain the pH is is great at the pH close to pKa.
<span>This is a </span>strong acid - strong base<span> <span>reaction. </span></span>HNO</span>₃ is the strong acid<span> <span>and </span></span>KOH is the strong
base<span>. </span><span>
H</span>⁺<span> in the HNO₃<span>
and </span></span>OH⁻<span> <span>of the KOH pair up and make </span></span>H₂O(l)<span>. </span><span>
NO</span>₃⁻<span> <span>and </span></span>K⁺<span> <span>pair up to make </span></span>KNO₃ salt<span>. </span><span>
<span>When writing chemical formulas </span>positive ion comes first<span> <span>and second
is negative ion. The charges should be switched. Since </span></span>positive ion has +1 and negative
ion has -1<span> <span>after
the switching off charges </span>the </span>product should be KNO</span>₃.<span>
Balance
equation is </span><span>
HNO</span>₃<span>(aq) + KOH(aq) → H</span>₂O(l) + KNO<span>₃(aq)</span><span> <span> 2. Salt is Ca(NO</span></span>₃)₂<span>
</span>This is a strong acid - strong
base<span> reaction. </span>HNO₃ is the strong acid<span> and </span>Ca(OH)₂ is the strong base<span>. </span><span> <span> H</span></span>⁺<span> in the HNO₃ and </span>OH⁻<span> of the Ca(OH)₂
pair up and make </span>H₂O(l)<span>. </span><span>
Ca²⁺
and </span>NO₃⁻<span> pair up to make </span>Ca(NO₃)₂ salt<span>. </span><span> <span> </span><span>Positive ion is </span>Ca²⁺<span>
which has </span></span>+2 charge<span> and negative ion is</span> NO₃⁻<span> <span>which has </span></span>-1 charge<span>. From switching the charges </span>Ca²⁺ gets 1<span> <span>while </span></span>NO₃⁻ gets 2.<span> Hence, the salt should be </span>Ca(NO₃)₂.<span>
Balanced equation
is </span>2HNO₃<span>(aq) + Ca(OH)</span>₂<span>(aq) → 2H</span>₂O(l) + Ca(NO<span>₃)₂(aq)</span><span> <span> 3. Salt is CaCl</span></span>₂<span>
This is a strong acid - strong base<span> reaction. </span>HCl is the
strong acid<span> and </span>Ca(OH)</span>₂ is the strong base<span>. </span><span> <span> H</span></span>⁺<span> in the HCl and </span>OH⁻<span> of the Ca(OH)₂
pair up and make </span>H₂O(l)<span>. </span><span>
Ca²⁺
and </span>Cl⁻<span> pair up to make </span>CaCl₂ salt<span>. </span><span> <span> </span><span>Positive ion is </span>Ca²⁺
which has </span>+2
charge<span> and negative ion is</span> Cl⁻<span> which has </span>-1
charge<span>. By switching the charges </span>Ca²⁺ gets 1<span> while </span>NO₃⁻ gets 2.<span> Hence, the salt should be </span>CaCl₂.<span>
Balance
equation is </span><span>2HCl(aq) + Ca(OH)</span>₂<span>(aq) → 2H</span>₂O(l) + CaCl₂<span>(aq)
4. Salt is KCl<span>
</span>This is a strong acid - strong base<span> reaction. </span>HCl is the
strong acid<span> and </span>KOH is
the strong base<span>. </span> <span> H</span></span>⁺<span> in the HCl and </span>OH⁻<span> of the KOH pair up and make </span>H₂O(l)<span>. </span><span>
K</span><span>⁺ and </span>Cl⁻<span> pair up to make </span>KCl salt<span>. </span><span> <span> </span><span>Positive ion is K</span></span><span>⁺ which has </span>+1
charge<span> and negative ion is</span> Cl⁻<span> which has </span>-1
charge<span>. By switching the charges </span>K⁺ gets 1<span> and </span>Cl⁻ also gets 1.<span> Hence, the salt should be </span>KCl.<span>
Balance
equation is </span><span>HCl(aq) + KOH(aq) → H</span>₂<span>O(l) + KCl(aq)</span>
Of any substance? What about two powders such as 1/2 cup of white flour, then mixing 1/2 cup of salt together with the flour. This would then form a more coarse mixture being that the two particles differ in shape.
Echo refers to the sound that is heard when a sound wave is reflected back from a surface. An echo sound is made when a sound wave traveled through the air, hit a hard surface and get reflected back. Generally, hard surfaces reflect sound wave while soft surfaces absorb sound waves. Reflected sound waves are used in application of some devices that are used in range and direction finding.
